Nature and Purpose:
Therefore, in this world he [man] must prepare himself for the life beyond. That which he needs in the world of the Kingdom must be obtained here. Just as he prepared himself in the world of the matrix by acquiring forces necessary in this sphere of existence, so, likewise, the indispensable forces of the divine existence must be potentially attained in this world.
What is he in need of in the Kingdom which transcends the life and limitation of this mortal sphere? That world beyond is a world of sanctity and radiance; therefore, it is necessary that in this world he should acquire these divine attributes. In that world there is need of spirituality, faith, assurance, the knowledge and love of God. These he must attain in this world so that after his ascension from the earthly to the heavenly Kingdom he shall find all that is needful in that eternal life ready for him.
That divine world is manifestly a world of lights; therefore, man has need of illumination here. That is a world of love; the love of God is essential. It is a world of perfections; virtues, or perfections, must be acquired. That world is vivified by the breaths of the Holy Spirit; in this world we must seek them. That is the Kingdom of everlasting life; it must be attained during this vanishing existence.
By what means can man acquire these things? How shall he obtain these merciful gifts and powers? First, through the knowledge of God. Second, through the love of God. Third, through faith. Fourth, through philanthropic deeds. Fifth, through self-sacrifice. Sixth, through severance from this world. Seventh, through sanctity and holiness. Unless he acquires these forces and attains to these requirements, he will surely be deprived of the life that is eternal. But if he possesses the knowledge of God, becomes ignited through the fire of the love of God, witnesses the great and mighty signs of the Kingdom, becomes the cause of love among mankind and lives in the utmost state of sanctity and holiness, he shall surely attain to second birth, be baptized by the Holy Spirit and enjoy everlasting existence.
(`Abdu’l-Baha: Promulgation of Universal Peace, p. 226)

…man must acquire heavenly qualities and attain divine attributes. He must become the image and likeness of God. He must seek the bounty of the eternal, become the manifestor of the love of God, the light of guidance, the tree of life and the depository of the bounties of God. That is to say, man must sacrifice the qualities and attributes of the world of nature for the qualities and attributes of the world of God. For instance, consider the substance we call iron. Observe its qualities; it is solid, black, cold. These are the characteristics of iron. When the same iron absorbs heat from the fire, it sacrifices its attribute of solidity for the attribute of fluidity. It sacrifices its attribute of darkness for the attribute of light, which is a quality of the fire. It sacrifices its attribute of coldness to the quality of heat which the fire possesses so that in the iron there remains no solidity, darkness or cold. It becomes illumined and transformed, having sacrificed its qualities to the qualities and attributes of the fire.
Likewise, man, when separated and severed from the attributes of the world of nature, sacrifices the qualities and exigencies of that mortal realm and manifests the perfections of the Kingdom, just as the qualities of the iron disappeared and the qualities of the fire appeared in their place.
Every man trained through the teachings of God and illumined by the light of His guidance, who becomes a believer in God and His signs and is enkindled with the fire of the love of God, sacrifices the imperfections of nature for the sake of divine perfections. Consequently, every perfect person, every illumined, heavenly individual stands in the station of sacrifice.
(`Abdu’l-Baha: Promulgation of Universal Peace, pp. 451-452)

Know thou that every soul is fashioned after the nature of God, each being pure and holy at his birth. Afterwards, however, the individuals will vary according to what they acquire of virtues or vices in this world. Although all existent beings are in their very nature created in ranks or degrees, for capacities are various, nevertheless every individual is born holy and pure, and only thereafter may he become defiled.
(`Abdu’l-Baha: Selections … `Abdu’l-Baha, p. 190)

It is only by the breath of the Holy Spirit that spiritual development can come about. No matter how the material world may progress, no matter how splendidly it may adorn itself, it can never be anything but a lifeless body unless the soul is within, for it is the soul that animates the body; the body alone has no real significance. Deprived of the blessings of the Holy Spirit the material body would be inert.
(`Abdu’l-Baha: Paris Talks, p. 133)

But the honor of the human kingdom is the attainment of spiritual happiness in the human world, the acquisition of the knowledge and love of God. The honor allotted to man is the acquisition of the supreme virtues of the human world. This is his real happiness and felicity. But if material happiness and spiritual felicity be conjoined, it will be “delight upon delight,” as the Arabs say.
(`Abdu’l-Baha: Promulgation of Universal Peace, p. 166)

Therefore, I exhort you to be devoted to your spiritual development. Just as you have striven along material lines and have attained to high degrees of worldly advancement, may you likewise become strengthened and proficient in the knowledge of God. May divine susceptibilities be increased and awakened; may your devotion to the heavenly Kingdom become intense. May you be the recipients of the impulses of the Holy Spirit, be assisted in the world of morality and attain ideal power so that the sublimity of the world of mankind may become apparent in you. Thus may you attain the highest happiness, the eternal life, the everlasting glory, the second birth, and become manifestations of the bestowals of God.
(`Abdu’l-Baha: Promulgation of Universal Peace, p. 206)

…The inestimable value of religion is that when a man is vitally connected with it, through a real and living belief in it and in the Prophet who brought it, he receives a strength greater than his own which helps him to develop his good characteristics and overcome his bad ones. The whole purpose of religion is to change not only our thoughts but our acts; when we believe in God and His Prophet and His teachings, we find we are growing even though we perhaps thought ourselves incapable of growth and change.
(Shoghi Effendi: Lights of Guidance, p. 508)

Effort is Required:
Success or failure, gain or loss, must, therefore, depend upon man’s own exertions. The more he striveth, the greater will be his progress.
(Baha’u’llah: Gleanings, pp. 81-82)

My holy, My divinely ordained Revelation may be likened unto an ocean in whose depths are concealed innumerable pearls of great price, of surpassing luster. It is the duty of every seeker to bestir himself and strive to attain the shores of this ocean, so that he may, in proportion to the eagerness of his search and the efforts he hath exerted, partake of such benefits as have been pre-ordained in God’s irrevocable and hidden Tablets.
(Baha’u’llah: Gleanings, p. 326)

Duty to Acquire Knowledge:
…man should know his own self and recognize that which leadeth unto loftiness or lowliness, glory or abasement, wealth or poverty.
(Baha’u’llah: Tablets of Baha’u’llah, p. 35)

Knowledge is as wings to man’s life, and a ladder for his ascent. Its acquisition is incumbent upon everyone.
(Baha’u’llah: Epistle to the Son of the Wolf, p. 26)

All blessings are divine in origin, but none can be compared with this power of intellectual investigation and research, which is an eternal gift producing fruits of unending delight. Man is ever partaking of these fruits. All other blessings are temporary; this is an everlasting possession. Even sovereignty has its limitations and overthrow; this is a kingship and dominion which none may usurp or destroy. Briefly, it is an eternal blessing and divine bestowal, the supreme gift of God to man. Therefore, you should put forward your most earnest efforts toward the acquisition of science and arts. The greater your attainment, the higher your standard in the divine purpose.
(`Abdu’l-Baha: Promulgation of Universal Peace, p. 50)

Duty to Assess Oneself:
O SON OF BEING! Bring thyself to account each day ere thou art summoned to a reckoning; for death, unheralded, shall come upon thee and thou shalt be called to give account for thy deeds.
(Baha’u’llah: Arabic Hidden Words, p. 31)

Let each morn be better than its eve and each morrow richer than its yesterday.
(Baha’u’llah: Tablets of Baha’u’llah, p. 138)

Let your thoughts dwell on your own spiritual development, and close your eyes to the deficiencies of other souls.
(`Abdu’l-Baha: Selections … `Abdu’l-Baha, p. 203)

The Benefits of Suffering:
Those who suffer most, attain to the greatest perfection.
Those who declare a wish to suffer much for Christ’s sake must prove their sincerity; those who proclaim their longing to make great sacrifices can only prove their truth by their deeds. Job proved the fidelity of his love for God by being faithful through his great adversity, as well as during the prosperity of his life. The apostles of Christ who steadfastly bore all their trials and sufferings – did they not prove their faithfulness? Was not their endurance the best proof?
These griefs are now ended.
Caiaphas lived a comfortable and happy life while Peter’s life was full of sorrow and trial; which of these two is the more enviable? Assuredly we should choose the present state of Peter, for he possesses immortal life whilst Caiaphas has won eternal shame. The trials of Peter tested his fidelity. Tests are benefits from God, for which we should thank Him. Grief and sorrow do not come to us by chance, they are sent to us by the Divine Mercy for our own perfecting.
While a man is happy he may forget his God; but when grief comes and sorrows overwhelm him, then will he remember his Father who is in Heaven, and who is able to deliver him from his humiliations.
Men who suffer not, attain no perfection. The plant most pruned by the gardeners is that one which, when the summer comes, will have the most beautiful blossoms and the most abundant fruit.
The labourer cuts up the earth with his plough, and from that earth comes the rich and plentiful harvest. The more a man is chastened, the greater is the harvest of spiritual virtues shown forth by him. A soldier is no good General until he has been in the front of the fiercest battle and has received the deepest wounds.
The prayer of the prophets of God has always been, and still is: Oh God, I long to lay down my life in the path to Thee! I desire to shed my blood for Thee, and to make the supreme sacrifice.
(`Abdu’l-Baha: Paris Talks, pp. 50-51)

We should not, however, forget that an essential characteristic of this world is hardship and tribulation and that it is by overcoming them that we achieve our moral and spiritual development. As the Master says, sorrow is like furrows, the deeper they go the more plentiful are the fruits we obtain.
(Shoghi Effendi: Living the Life, p. 4)

Other Guidelines for Spiritual Growth:
Incline your hearts, O people of God, unto the counsels of your true, your incomparable Friend. The Word of God may be likened unto a sapling, whose roots have been implanted in the hearts of men. It is incumbent upon you to foster its growth through the living waters of wisdom, of sanctified and holy words, so that its root may become firmly fixed and its branches may spread out as high as the heavens and beyond.
(Baha’u’llah: Gleanings, p. 97)

Therefore, we learn that nearness to God is possible through devotion to Him, through entrance into the Kingdom and service to humanity; it is attained by unity with mankind and through loving-kindness to all; it is dependent upon investigation of truth, acquisition of praiseworthy virtues, service in the cause of universal peace and personal sanctification. In a word, nearness to God necessitates sacrifice of self, severance and the giving up of all to Him. Nearness is likeness.
(`Abdu’l-Baha: Promulgation of Universal Peace, p. 148)

Truthfulness is the foundation of all human virtues. Without truthfulness progress and success, in all the worlds of God, are impossible for any soul. When this holy attribute is established in man, all the divine qualities will also be acquired.
(`Abdu’l-Baha: Trustworthiness, p. 338)

My meaning is this, that in every aspect of life, purity and holiness, cleanliness and refinement, exalt the human condition and further the development of man’s inner reality. Even in the physical realm, cleanliness will conduce to spirituality, as the Holy Writings clearly state. And although bodily cleanliness is a physical thing, it hath, nevertheless, a powerful influence on the life of the spirit.
(`Abdu’l-Baha: Selections … `Abdu’l-Baha, pp. 146-147)

For the core of religious faith is that mystic feeling which unites man with God. This state of spiritual communion can be brought about and maintained by means of meditation and prayer. And this is the reason why Baha’u’llah has so much stressed the importance of worship.
It is not sufficient for a believer merely to accept and observe the teachings. He should, in addition, cultivate the sense of spirituality which he can acquire chiefly by means of prayer…
The believers, particularly the young ones, should therefore fully realize the necessity of praying. For prayer is absolutely indispensable to their inner spiritual development, and this, as already stated, is the very foundation and purpose of the religion of God.
(Shoghi Effendi: Lights of Guidance, p. 544)

The thing the … believers must do is to deepen themselves in the Covenants of Baha’u’llah and Abdu’l-Baha. Mere intellectual understanding of the Teachings is not enough. Deep spirituality is essential, and the foundation of true spirituality is steadfastness in the Covenant.
(Shoghi Effendi: Lights of Guidance, p. 543)

The only people who are truly free of the “dross of self” are the Prophets, for to be free of one’s ego is a hall-mark of perfection. We humans are never going to become perfect, for perfection belongs to a realm we are not destined to enter. However, we must constantly mount higher, seek to be more perfect.
The ego is the animal in us, the heritage of the flesh which is full of selfish desires. By obeying the laws of God, seeking to live the life laid down in our teachings, and prayer and struggle, we can subdue our egos.
(Shoghi Effendi: Unfolding Destiny, p. 453)

Baha’u’llah has stated quite clearly in His Writings the essential requisites for our spiritual growth, and these are stressed again and again by Abdu’l-Baha in His Talks and Tablets. One can summarise them briefly in this way:
1. The recital each day of one of the Obligatory Prayers with pure-hearted devotion.
2. The regular reading of the Sacred Scriptures, specifically at least each morning and evening, with reverence, attention and thought.
3. Prayerful meditation on the teachings, so that we may understand them more deeply, fulfil them more faithfully, and convey them more accurately to others.
4. Striving every day to bring our behaviour more into accordance with the high standards that are set forth in the Teachings.
5. Teaching the Cause of God.
6. Selfless service in the work of the Cause and in the carrying on of our trade or profession.
(The Universal House of Justice: Lights of Guidance, p. 541)

Spiritual Growth in the Next World:
Know thou of a truth that the soul, after its separation from the body, will continue to progress until it attaineth the presence of God, in a state and condition which neither the revolution of ages and centuries, nor the changes and chances of this world, can alter. It will endure as long as the Kingdom of God, His sovereignty, His dominion and power will endure. It will manifest the signs of God and His attributes, and will reveal His loving-kindness and bounty.
(Baha’u’llah: Gleanings, pp. 155-156)

Man is destined by God to undergo a spiritual development that extends throughout eternity. His life upon this earth is only the first stage of that development. When we outgrow our physical form, and are considered by God ready to reap the fruit of our spiritual development, we proceed to the other world. We term it death only because of our shortsightedness. A more proper term would be `a more abundant life’.
(Shoghi Effendi: Lights of Guidance, p. 204)