From the Writings of Baha’u’llah:
And now concerning thy question regarding the soul of man and its survival after death. 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. The movement of My Pen is stilled when it attempteth to befittingly describe the loftiness and glory of so exalted a station.
The honor with which the Hand of Mercy will invest the soul is such as no tongue can adequately reveal, nor any other earthly agency describe. Blessed is the soul which, at the hour of its separation from the body, is sanctified from the vain imaginings of the peoples of the world. Such a soul liveth and moveth in accordance with the Will of its Creator, and entereth the all-highest Paradise. The Maids of Heaven, inmates of the loftiest mansions, will circle around it, and the Prophets of God and His chosen ones will seek its companionship. With them that soul will freely converse, and will recount unto them that which it hath been made to endure in the path of God, the Lord of all worlds. If any man be told that which hath been ordained for such a soul in the worlds of God, the Lord of the throne on high and of earth below, his whole being will instantly blaze out in his great longing to attain that most exalted, that sanctified and resplendent station…
The nature of the soul after death can never be described, nor is it meet and permissible to reveal its whole character to the eyes of men. The Prophets and Messengers of God have been sent down for the sole purpose of guiding mankind to the straight Path of Truth. The purpose underlying their revelation hath been to educate all men, that they may, at the hour of death, ascend, in the utmost purity and sanctity and with absolute detachment, to the throne of the Most High. The light which these souls radiate is responsible for the progress of the world and the advancement of its peoples. They are like unto leaven which leaveneth the world of being, and constitute the animating force through which the arts and wonders of the world are made manifest. Through them the clouds rain their bounty upon men, and the earth bringeth forth its fruits. All things must needs have a cause, a motive power, an animating principle. These souls and symbols of detachment have provided, and will continue to provide, the supreme moving impulse in the world of being.
The world beyond is as different from this world as this world is different from that of the child while still in the womb of its mother. When the soul attaineth the Presence of God, it will assume the form that best befitteth its immortality and is worthy of its celestial habitation. Such an existence is a contingent and not an absolute existence, inasmuch as the former is preceded by a cause, whilst the latter is independent thereof. Absolute existence is strictly confined to God, exalted be His glory. Well is it with them that apprehend this truth. Wert thou to ponder in thine heart the behavior of the Prophets of God thou wouldst assuredly and readily testify that there must needs be other worlds besides this world. The majority of the truly wise and learned have, throughout the ages, as it hath been recorded by the Pen of Glory in the Tablet of Wisdom, borne witness to the truth of that which the holy Writ of God hath revealed. Even the materialists have testified in their writings to the wisdom of these divinely-appointed Messengers, and have regarded the references made by the Prophets to Paradise, to hell fire, to future reward and punishment, to have been actuated by a desire to educate and uplift the souls of men.
Consider, therefore, how the generality of mankind, whatever their beliefs or theories, have recognized the excellence, and admitted the superiority, of these Prophets of God. These Gems of Detachment are acclaimed by some as the embodiments of wisdom, while others believe them to be the mouthpiece of God Himself. How could such Souls have consented to surrender themselves unto their enemies if they believed all the worlds of God to have been reduced to this earthly life? Would they have willingly suffered such afflictions and torments as no man hath ever experienced or witnessed?
Gleanings from the Writings of Bahá’u’lláh (Wilmette: Bahá’í Publishing Trust, 1983), LXXIII, pp. 155-158