From: http://www.northill.demon.co.uk/bahai/intro1.htm (http://www.northill.demon.co.uk/bahai/intro1.htm)
Extracted and condensed from A Short Introduction to the Bahá'í Faith
Bahá'u'lláh's writings indicate that, if we want happiness and contentment, we must do precisely the opposite to what we are constantly being urged to do by many of those around us. He advises us:
Dissipate not the wealth of your precious lives in the pursuit of evil and corrupt affection, nor let your endeavours be spent in promoting your personal interest.
Referring to the illusion that wealth is of itself of any value to human happiness and development, Bahá'u'lláh says:
Thou dost wish for gold and I desire thy freedom from it. Thou thinkest thyself rich in its possession, and I recognize thy wealth in thy sanctity therefrom. By My life! This is My knowledge, and that is thy fancy; how can My way accord with thine?
Our belief that we can gain happiness by accumulating wealth and power or by indulging our sensual or material passions is due to the fact that we are deluded by the physical world that surrounds us. It seems so immediate and `real' that it is easy to think that it is the most important thing in our lives. The pressing immediacy and vividness of this world are veils hiding its emptiness. According to Bahá'u'lláh:
The world is but a show, vain and empty, a mere nothing, bearing the semblance of reality. Set not your affections upon it . . . Verily I say, the world is like the vapour in a desert, which the thirsty dreameth to be water and striveth after it with all his might, until when he cometh unto it, he findeth it to be mere illusion. 
This world and all that it promises are impermanent and with us for only a short time. We should not therefore grow attached to what will eventually fade and wither away:
These few brief days shall pass away, this present life shall vanish from our sight; the roses of this world shall be fresh and fair no more, the garden of this earth's triumphs and delights shall droop and fade. The spring season of life shall turn into the autumn of death, the bright joy of palace halls give way to moonless dark within the tomb. And therefore is none of this worth loving at all, and to this the wise will not anchor his heart (`Abdu'l-Bahá). 
We should try to change ourselves before the short time that we have on this earth comes to an end. Bahá'u'lláh urges us to cut ourselves free from the attractions of this world and the pursuit of selfish aims: "O My Servant! Free thyself from the fetters of this world, and loose thy soul from the prison of self. Seize thy chance, for it will come to thee no more."
If we are to find and understand the knowledge which leads to lasting happiness and contentment, we must search for it. Our search, however, should not be among the things of this world, which only lead to sadness and suffering. Rather we must make our search a spiritual quest. Bahá'u'lláh has likened the search to a spiritual journey and he has described how we must set about this journey.
The first condition for success in the search is patience and perseverance.
Without patience the wayfarer on this journey will reach nowhere and attain no goal. Nor should he ever be downhearted; if he strive for a hundred thousand years and yet fail to behold the beauty of the Friend, he should not falter . . . 
The second condition for success is to search with an open mind. We must be ready to set aside our fondest ideas and our preconceived notions:
It is incumbent on these servants that they cleanse the heart--which is the wellspring of divine treasures--from every marking, and that they turn away from imitation, which is following the traces of their forefathers and sires . . . Nor shall the seeker reach his goal unless he sacrifice all things. That is, whatever he hath seen, and heard, and understood, all must he set at naught, that he may enter the realm of the spirit, which is the City of God.
The third condition is an intense desire for the goal of the quest, an ardour or burning passion to achieve the objective. For the journey may be long and hard and there will be the many distractions of our daily lives to tempt us away.
The true seeker hunteth naught but the object of his quest, and the lover hath no desire save union with his beloved. . . Labour is needed, if we are to seek Him; ardour is needed, if we are to drink of the honey of reunion with Him; and if we taste of this cup, we shall cast away the world.
On this journey the traveller abideth in every land and dwelleth in every region. In every face, he seeketh the beauty of the Friend; in every country he looketh for the Beloved. He joineth every company, and seeketh fellowship with every soul, that haply in some mind he may uncover the secret of the Friend, or in some face he may behold the beauty of the Loved One.
Our first step on this journey is to detach ourselves from the attractions of this physical world. It is our clinging to these things of the physical world that blinds us to spiritual reality and holds back our spiritual progress. We must try to free ourselves from this:
Disencumber yourselves of all attachment to this world and the vanities thereof. Beware that ye approach them not, inasmuch as they prompt you to walk after your own lusts and covetous desires, and hinder you from entering the straight and glorious Path. (Bahá'u'lláh). 
It is not only the physical things of this world to which we cling. Bahá'u'lláh also calls upon people to shatter "the idols of their vain imaginings."
Even as the swiftness of lightning ye have passed by the Beloved One, and have set your hearts on satanic fancies. Ye bow the knee before your vain imagining, and call it truth. Ye turn your eyes towards the thorn, and name it a flower. Not a pure breath have ye breathed, nor hath the breeze of detachment been wafted from the meadows of your hearts. Ye have cast to the winds the loving counsels of the Beloved and have effaced them utterly from the tablet of your hearts, and even as the beasts of the field, ye move and have your being within the pastures of desire and passion. 
The process of detaching ourselves from our love for the attractions of this world is, however, a painful one. It is for this reason that Bahá'u'lláh says that if our hearts are attracted by love for the spiritual world then our companion in the course of our spiritual journey is pain. And yet this pain, because its result is joy and contentment, should be welcomed.
Love setteth a world aflame at every turn, and he wasteth every land where he carrieth his banner . . . He hath bound a myriad victims in his fetters, wounded a myriad wise men with his arrow. Know that every redness in the world is from his anger, and every paleness in men's cheeks is from his poison. He yieldeth no remedy but death, he walketh not save in the valley of the shadow; yet sweeter than honey is his venom on the lover's lips, and fairer his destruction in the seeker's eyes than a hundred thousand lives.
This pain, Bahá'u'lláh says, is caused by the burning away of the veils of illusion that have kept us bound to this world and away from the spiritual world. It is through this burning that the spirit is purified and a love arises for the spiritual world. Once these veils have been removed, then we see the world with different eyes; we discern a new meaning in the events of our lives and in everything around us.
His inner eyes will open and he will privily converse with his Beloved; he will set ajar the gate of truth and piety, and shut the doors of vain imaginings. He . . . seeth war as peace, and findeth in death the secrets of everlasting life . . . He beholdeth justice in injustice, and in justice, grace. In ignorance he findeth many a knowledge hidden, and in knowledge a myriad wisdoms manifest. He breaketh the cage of the body and the passions, and consorteth with the people of the immortal realm . . . And if he meeteth with injustice he shall have patience, and if he cometh upon wrath he shall manifest love.
What is the reason that we are upon the earth? What is the purpose of our lives here? Such questions have been the theme of the meditations and speculations of many philosophers and religious leaders down the ages. To understand the Bahá'í view on such questions, however, it is necessary to examine first the Bahá'í teachings on the true nature of a human being.
The Bahá'í scriptures state that the human being is spiritually a different order of being from the animal and all other beings. Bahá'u'lláh says that, whereas everything in creation is capable of reflecting some of the divine attributes, human beings alone have the capacity to reflect them all:
Upon the inmost reality of each and every created thing He hath shed the light of one of His names, and made it a recipient of the glory of one of His attributes. Upon the reality of man, however, He hath focused the radiance of all of His names and attributes, and made it a mirror of His own Self. Alone of all created things man hath been singled out for so great a favour, so enduring a bounty.
Our purpose in life, therefore, is to develop this potential and show these divine attributes in our actions. During our lives here on earth, we must try to acquire as many of these divine attributes as possible and to perfect them. Human beings have two sides to their nature, a lower aspect which is concerned with the material or animal side of our life, and a higher aspect which is the spiritual side. It is this second higher aspect that makes us truly human. `Abdu'l-Bahá says that we must constantly struggle to ensure that our higher side overcomes our animal side.
Then if the divine power in man, which is his essential perfection, overcomes the satanic power, which is absolute imperfection, he becomes the most excellent among the creatures; but if the satanic power overcomes the divine power, he becomes the lowest of the creatures.
What are these virtues that we must acquire to become truly human, to achieve lasting contentment and happiness? They are numerous and only a few will be considered here.
Bahá'u'lláh places great importance on our developing justice as a personal quality. The ability to be just and equitable in our assessment of situations and in our dealings with others is reckoned by Bahá'u'lláh as the "most fundamental among human virtues." This is because "the evaluation of all things must needs depend upon it."  Therefore, "The essence of all that We have revealed for thee is Justice, is for man to free himself from idle fancy and imitation, discern with the eye of oneness His glorious handiwork, and look into all things with a searching eye."
The best beloved of all things in My sight is Justice. By its aid thou shalt see with thine own eyes and not through the eyes of others, and shalt know of thine own knowledge and not through the knowledge of thy neighbour. Ponder this in thy heart; how it behooveth thee to be. Verily justice is My gift to thee and the sign of My loving-kindness. Set it then before thine eyes.
Part of justice is being fair in the way that one treats others: to choose "for thy neighbour that which thou choosest for thyself" (Bahá'u'lláh  ); not "to deny any soul the reward due to him" (Bahá'u'lláh  ); and "to respect the rights of all men (`Abdu'l-Bahá  )."
Human beings have a great capacity for love. `Abdu'l-Bahá says that:
There are many ways of expressing the love principle; there is love for the family, for the country, for the race, there is political enthusiasm . . . These are all ways and means of showing the power of love.
He warns, however, that these expressions of love are of a limited nature and may in fact also arouse hate.
The love of family is limited . . . Frequently members of the same family disagree, and even hate each other. Patriotic love is finite; the love of one's country causing hatred of all others, is not perfect love! . . . The love of race is limited . . . To love our own race may mean hatred of all others, and even people of the same race often dislike each other . . . Political love also is much bound up with hatred of one party for another . . . All these ties of love are imperfect. It is clear that limited material ties are insufficient to adequately express the universal love.
Real love, the spiritual love to which human beings should aspire, should be unlimited and universal:
Love is unlimited, boundless, infinite! Material things are limited, circumscribed, finite. You cannot adequately express infinite love by limited means. The perfect love needs anunselfish instrument, absolutely freed from fetters of every kind . . . The great unselfish love for humanity is bounded by none of these imperfect, semi-selfish bonds; this is the one perfect love, possible to all mankind, and can only be achieved by the power of the Divine Spirit. No worldly power can accomplish the universal love.
Associated with love are several other qualities that Bahá'u'lláh praises and that should govern our relations with others. Among these are kindliness, friendliness, compassion, charity, forebearence, and generosity.
iii. Trustworthiness and truthfulness
Trustworthiness is the basis for all of human social life. In the writings of Bahá'u'lláh, it is accorded great importance since "the stability of every affair hath depended and doth depend upon it."  It is described as "the greatest portal leading unto the tranquillity and security of the people"  , and the "supreme instrument for the prosperity of the world." 
Truthfulness is the"foundation of all human virtues" (Bahá'u'lláh  ). This is because it, together with justice, protects us from self-deception and enables us to measure our spiritual progress. It forestalls hypocrisy and insincerity.
Beautify your tongues, O people, with truthfulness, and adorn your souls with the ornament of honesty. Beware, O people, that ye deal not treacherously with any one. (Bahá'u'lláh). 
Part of the truthfulness and sincerity that Bahá'u'lláh advocates is for his followers to act in accordance with the high ideals that they profess (see below).
iv. Purity and Chastity
Purity is not a word that is fashionable in the world today. To a person who is struggling to develop spiritually, it signifies the attempt to free oneself from self-interest, from the corruption and degeneracy of the modern world, and from such base instincts as envy, malice, pride, lust, hypocrisy and hatred. The aim, however, is not to achieve a haughty puritanism or to become priggish; nor is a severe asceticism considered desirable.
It must be remembered, however, that the maintenance of such a high standard of moral conduct is not to be associated or confused with any form of asceticism, or of excessive and bigoted puritanism. The standard inculcated by Bahá'u'lláh, seeks, under no circumstances, to deny anyone the legitimate right and privilege to derive the fullest advantage and benefit from the manifold joys, beauties, and pleasures with which the world has been so plentifully enriched by an All-Loving Creator. (Shoghi Effendi) 
To advance along the road of purity frees one from the insistent demands of our lower nature. Since these demands can never be satisfied, advancing along this path in fact leads to freedom and contentment.
Live then the days of thy life, that are less than a fleeting moment, with thy mind stainless, thy heart unsullied, thy thoughts pure, and thy nature sanctified, so that, free and content, thou mayest put away this mortal frame, and repair unto the mystic paradise and abide in the eternal kingdom for evermore. (Bahá'u'lláh) 
Chastity is the sexual aspect of purity. Again it should not be mistaken for prudery or thesuppression of sexuality. It is rather the acknowledgment that the sexual instinct is strong and requires some degree of conscious control.
The Bahá'í Faith recognizes the value of the sex impulse, but condemns its illegitimate and improper expressions such as free love, companionate marriage and others, all of which it considers positively harmful to man and to the society in which he lives. The proper use of the sex instinct is the natural right of every individual, and it is precisely for this purpose that the institution of marriage has been established. The Bahá'ís do not believe in the suppression of the sex impulse but in its regulation and control. (Shoghi Effendi) 
This control should ideally extend not just to actions but even to one's thoughts.
And if he met the fairest and most comely of women, he would not feel his heart seduced by the least shadow of desire for her beauty. Such an one, indeed, is the creation of spotless chastity. (Bahá'u'lláh) 
v. Actions not words
The Bahá'í writings emphasize that the result of our efforts on the spiritual path must be seen in our character and our actions. Bahá'u'lláh calls upon his followers to match their actions to theirwords: "Let deeds, not words, be your adorning."  It is easy for anyone to speak pious words and to utter sanctimonious platitudes. But Bahá'u'lláh says that "the essence of faith is fewness of words and abundance of deeds." What distinguishes the person who is truly advancing on the spiritual path is their character and their actions.
Guidance hath ever been given by words, and now it is given by deeds. Every one must show forth deeds that are pure and holy, for words are the property of all alike, whereas such deeds as these belong only to Our loved ones. Strive then with heart and soul to distinguish yourselves by your deeds. 
As has already been said above, these Bahá'í teachings should not be regarded as advocating asceticism or a rigid puritanism. Both Bahá'u'lláh and `Abdu'l-Bahá are recorded as having enjoyed laughter and joking. Bahá'u'lláh has even said that we can enjoy the things of this world as long as we do not allow them to come between us and our quest for the spiritual and the divine:
Should a man wish to adorn himself with the ornaments of the earth, to wear its apparels, or partake of the benefits it can bestow, no harm can befall him, if he alloweth nothing whatever to intervene between him and God, for God hath ordained every good thing, whether created in the heavens or in the earth, for such of His servants as truly believe in Him. Eat ye, O people, of the good things which God hath allowed you, and deprive not yourselves from His wondrous bounties. 
One important attribute, one characteristic that distinguishes those who are truly developing their human and spiritual characteristics is their willingness and ability to serve others. It is, as Bahá'u'lláh has said, the characteristic of being truly human.
That one indeed is a man who, today, dedicateth himself to the service of the entire human race. The Great Being saith: Blessed and happy is he that ariseth to promote the best interests of the peoples and kindreds of the earth. 
Part of our service is the work that we do to earn our living. Bahá'u'lláh makes it a duty for all his followers to engage in some useful occupation and raises the status of such work to the level of worship.
It is enjoined upon each one of you to engage in some occupation, such as a craft, a trade or the like. We have exalted your engagement in such work to the rank of worship . . . Waste not your hours in idleness and sloth, but occupy yourselves with what will profit you and others. 
vii. Can we reach these goals?
Some may question whether these goals that Bahá'u'lláh has set are too high and whether Bahá'ís are being too idealistic in trying to pursue them. Others may assert that the path that Bahá'u'lláh describes is too austere and sombre a way of life for most people.
There can be no intellectual answer to such objections. It is only by the experience of trying to live according to these teachings that one can see whether these objections have any basis or not. In writing of the need to plunge oneself into the experience to know what it is like rather than to stand on the edge observing, Bahá'u'lláh relates:
The story is told of a mystic knower, who went on a journey with a learned grammarian as his companion. They came to the shore of the Sea of Grandeur. The knower straightway flung himself into the waves, but the grammarian stood lost in his reasonings, which were as words that are written on water. The knower called out to him, "Why dost thou not follow?" The grammarian answered, "O Brother, I dare not advance. I must needs go back again." Then the knower cried, "Forget what thou didst read in . . . books . . . and cross the water." 
Bahá'u'lláh does not expect human beings to be perfect from the outset, only that we take the first step and advance little by little. The path is long, hard and narrow, and Bahá'u'lláh has explained that patience and perseverance are needed and that some degree of pain is inevitable (see above). Bahá'u'lláh has, however, promised guidance and support from the spiritual world for those who seek to follow it. Part of this guidance and support comes from such spiritual exercises as prayer and meditation . If we live with our thoughts concentrated upon the spiritual world, then the misfortunes and difficulties that we experience do not affect us for there is an underlying contentment and joy.
. . . the trials which beset our every step, all our sorrow, pain, shame and grief, are born in the world of matter; whereas the spiritual Kingdom never causes sadness. A man living with his thoughts in this Kingdom knows perpetual joy. The ills all flesh is heir to do not pass him by, but they only touch the surface of his life, the depths are calm and serene. (`Abdu'l-Bahá) 
The Bahá'í teachings see human beings as being both physical and spiritual in nature. Health is therefore seen to be something that can only be achieved if there is well-being and balance in both the physical and the spiritual aspects of a person's life. We can achieve spiritual health by following the spiritual path described above. If we reach the stage indicated above where we experience lasting contentment and joy, this clearly will also have a positive effect on our mental and physical health.
Indeed one must look further than just the individual. For, as `Abdu'l-Bahá has said, "every part of the universe is connected with every other part by ties that are very powerful and admit of no imbalance, nor any slackening whatever." Therefore the inter-relationships of individuals with those around them and with their environment will also affect their health--and, if this is not in balance, may cause disease. In this wider sense, many of the social teachings of Bahá'u'lláh (such as the elimination of extremes of poverty, the advancement of the social role of women, universal education, see section 3) can be considered to be related to health.
Since human beings have both a physical and a spiritual aspect, illness can have both physical and spiritual causes and healing can be achieved by both physical and spiritual means:
There are two ways of healing sickness, material means and spiritual means. The first is by the treatment of physicians; the second consisteth in prayers offered by the spiritual ones to God and in turning to Him. Both means should be used and practised. Illnesses which occur because of physical causes should be treated by doctors with medical remedies; those which are due to spiritual causes disappear through spiritual means. Thus an illness caused by affliction, fear, nervous impressions, will be healed more effectively by spiritual rather than by physical treatment. Hence, both kinds of treatment should be followed; they are not contradictory. Therefore thou shouldst also accept physical remedies inasmuch as these too have come from the mercy and favour of God, Who hath revealed and made manifest medical science so that His servants may profit from this kind of treatment also. Thou shouldst give equal attention to spiritual treatments, for they produce marvellous effects. (`Abdu'l-Bahá)