THOU hast asked Me concerning the nature of the soul. Know, verily, that the soul is a sign of God, a heavenly gem whose reality the most learned of men hath failed to grasp, and whose mystery no mind, however acute, can ever hope to unravel. It is the first among all created things to declare the excellence of its Creator, the first to recognize His glory, to cleave to His truth, and to bow down in adoration before Him. If it be faithful to God, it will reflect His light, and will, eventually, return unto Him. If it fail, however, in its allegiance to its Creator, it will become a victim to self and passion, and will, in the end, sink in their depths.         

—— Gleanings from the Writings of Bahá’u’lláh 82

The human soul is, in its essence, one of the signs of God, a mystery among His mysteries. It is one of the mighty signs of the Almighty, the harbinger that proclaimeth the reality of all the worlds of God. Within it lieth concealed that which the world is now utterly incapable of apprehending.         

—— Gleanings from the Writings of Bahá’u’lláh 82

O Brother, if we ponder each created thing, we shall witness a myriad perfect wisdoms and learn a myriad new and wondrous truths. One of the created phenomena is the dream. Behold how many secrets are deposited therein, how many wisdoms treasured up, how many worlds concealed. Observe, how thou art asleep in a dwelling, and its doors are barred; on a sudden thou findest thyself in a far-off city, which thou enterest without moving thy feet or wearying thy body; without using thine eyes, thou seest; without taxing thine ears, thou hearest; without a tongue, thou speakest. And perchance when ten years are gone, thou wilt witness in the outer world the very things thou hast dreamed tonight.

—— Bahá’u’lláh, The Seven Valleys And the Four Valleys

 The human soul is exalted above all egress and regress. It is still, and yet it soareth; it moveth, and yet it is still. It is, in itself, a testimony that beareth witness to the existence of a world that is contingent, as well as to the reality of a world that hath neither beginning nor end. Behold how the dream thou hast dreamed is, after the lapse of many years, re-enacted before thine eyes. Consider how strange is the mystery of the world that appeareth to thee in thy dream. Ponder in thine heart upon the unsearchable wisdom of God, and meditate on its manifold revelations….

—— Gleanings from the Writings of Bahá’u’lláh 82

 the world that which thou hast experienced in thy dream hath neither beginning nor end. It would be true if thou wert to contend that this same world is, as decreed by the All-Glorious and Almighty God, within thy proper self and is wrapped up within thee. It would equally be true to maintain that thy spirit, having transcended the limitations of sleep and having stripped itself of all earthly attachment, hath, by the act of God, been made to traverse a realm which lieth hidden in the innermost reality of this world. Verily I say, the creation of God embraceth worlds besides this world, and creatures apart from these creatures. In each of these worlds He hath ordained things which none can search except Himself, the All-Searching, the All-Wise.

—— Gleanings from the Writings of Bahá’u’lláh 79

The soul of man is exalted above, and is independent of all infirmities of body or mind.
—— Gleanings from the Writings of Bahá’u’lláh 80

When man is asleep, his soul can, in no wise, be said to have been inherently affected by any external object. It is not susceptible of any change in its original state or character. Any variation in its functions is to be ascribed to external causes. It is to these external influences that any variations in its environment, its understanding, and perception should be attributed.

—— Gleanings from the Writings of Bahá’u’lláh 82

here are many wisdoms to ponder in the dream. First, what is this world, where without eye and ear and hand and tongue a man puts all of these to use? Second, how is it that in the outer world thou seest today the effect of a dream, when thou didst vision it in the world of sleep some ten years past?
Consider the difference between these two worlds and the mysteries which they conceal, that thou mayest attain to divine confirmations and heavenly discoveries and enter the regions of holiness.
—— Bahá’u’lláh, The Seven Valleys And the Four Valleys