How a human soul could become like “a divine physician to mankind”

If in this day a soul shall act according to the precepts and the counsels of God, he will serve as a divine physician to mankind, and like the trump of Isráfíl [1], he will call the dead of this contingent world to life; for the confirmations of the Abhá Realm are never interrupted, and such a virtuous soul hath, to befriend him, the unfailing help of the Company on high. Thus shall a sorry gnat become an eagle in the fulness of his strength, and a feeble sparrow change to a royal falcon in the heights of ancient glory.

Wherefore, look not on the degree of your capacity, ask not if you are worthy of the task: rest ye your hopes on the help and loving-kindness, the favours and bestowals of Bahá’u’lláh—may my soul be offered up for His friends! Urge on the steed of high endeavour over the field of sacrifice, and carry away from this wide arena the prize of divine grace. (‘Abdu’l-Baha, ‘Selections from the Writings of ‘Abdu’l-Baha’)

[1] Believed to be the angel appointed to sound the trumpet on the Day of Resurrection to raise the dead at the bidding of the Lord.

The “human soul comes into being at the time of conception…”

... the Bahá'í Writings affirm that the human soul comes into being at the time of conception. However, they do not clearly define the exact biological moment and nature of the event described as conception and this may, indeed, be a question that is insoluble by human thought or investigation, since it relates to mysteries of the spiritual world and the nature of the soul itself. (From a letter dated 6 February 1997 written on behalf of the Universal House of Justice to a National Spiritual Assembly; compilation ‘Reproduction and other Biological Subjects ‘, prepared by the Research Department of the Universal House of Justice)

The light that pure, sanctified, and detached souls radiate after their separation from the body “is responsible for the progress of the world and the advancement of its peoples”

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. (Baha'u'llah, Gleanings from the Writings of Baha'u'llah)

The perception of the rational soul

The first condition of perception in the world of nature is the perception of the rational soul. In this perception and in this power all men are sharers, whether they be neglectful or vigilant, believers or deniers. This human rational soul is God's creation; it encompasses and excels other creatures; as it is more noble and distinguished, it encompasses things. The power of the rational soul can discover the realities of things, comprehend the peculiarities of beings, and penetrate the mysteries of existence. All sciences, knowledge, arts, wonders, institutions, discoveries and enterprises come from the exercised intelligence of the rational soul. 
(‘Abdu’l-Baha, "Some Answered Questions"; The Compilation of Compilations, vol. III, The Importance of Arts in Promoting the Faith)

The “Kingdom is the real world, and this nether place is only its shadow stretching out.”

Know thou that the Kingdom is the real world, and this nether place is only its shadow stretching out. A shadow hath no life of its own; its existence is only a fantasy, and nothing more; it is but images reflected in water, and seeming as pictures to the eye. 
(‘Abdu'l-Baha, ‘Selections from the Writings of Abdu'l-Baha’)

The “form” of the soul that is suitable for its immortality

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. 
(Baha'u'llah, Gleanings from the Writings of Baha'u'llah)

When “the souls that are not good die, they go entirely away from this earth and so cannot influence anyone.”

Question: Are there "earthbound" souls who try to have, and do have, an influence over people, sometimes taking entire possession of their wills?

'Abdu'l-Baha answered, "There are no earthbound souls. When the souls that are not good die, they go entirely away from this earth and so cannot influence anyone. They are spiritually dead. Their thoughts can have influence only while they are alive on the earth. Caiaphas had great influence during his life, but as soon as he died, his influence ceased. It was of this kind that Christ said, 'Let the dead bury their dead.' But the good souls are given eternal life, and sometimes God permits their thoughts to reach the earth to help the people." 
(From a table talk by ‘Abdu’l-Baha, ‘Daily Lessons Received at Akka January 1908”, by Helen Goodall and Ella Goodall Cooper)

The “soul is a sign of God, a heavenly gem …whose mystery no mind, however acute, can ever hope to unravel.”

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 fails, 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. 
(Baha'u'llah, Gleanings from the Writings of Baha'u'llah)

The effect of gossip and backbiting on one’s soul

"... Backbiting quencheth the light of the heart, and extinguisheth the life of the soul." 
(Bahá'u'lláh, 'The Kitáb-i-Íqán')  

“The human soul is an essence spiritual in entity and material or physical in function.”

The human soul is an essence spiritual in entity and material or physical in function. It is defined as essence because it is independent in itself, while the body is accidental and dependent upon the soul. 
(‘Abdu’l-Baha, from a talk, quoted by Lua Getsinger in her talk in San Francisco on December 17, 1911)(To see the transcript of the entire talk please visit Baha’i Talks, Messages and Articles)

The “human soul” is that “all-unifying agency” that connects “the various organs and members, the parts and elements, that constitute the body of man” and “causeth them to function in perfect harmony and with absolute regularity, thus making the continuation of life possible.”

By nature is meant those inherent properties and necessary relations derived from the realities of things. And these realities of things, though in the utmost diversity, are yet intimately connected one with the other. For these diverse realities an all-unifying agency is needed that shall link them all one to the other. For instance, the various organs and members, the parts and elements, that constitute the body of man, though at variance, are yet all connected one with the other by that all-unifying agency known as the human soul, that causeth them to function in perfect harmony and with absolute regularity, thus making the continuation of life possible. The human body, however, is utterly unconscious of that all-unifying agency, and yet acteth with regularity and dischargeth its functions according to its will. 
(‘Abdu’l-Baha, ‘Tablet to August Forel)

To train our soul in this life so that “at the hour of death, [it will] ascend, in the utmost purity and sanctity and with absolute detachment.”

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. 
(Baha'u'llah, Gleanings from the Writings of Baha'u'llah)

Vastness of next world compared to this world

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. 
(Baha'u'llah, Gleanings from the Writings of Baha'u'llah)

Receiving “eternal life” from the divine Spirit

O maid-servant of God! The human spirit hath an impression and effect in the world, but the divine Spirit giveth life to the souls and conferreth eternal life upon those who are attracted to the fragrances of God. This is the Great Cause from the Kingdom of thy Lord.

Be attached to this New Spirit which hath effective power in the realities of things and creates new creatures. 
(‘Abdu’l-Baha, ‘Tablets of ‘Abdu’l-Baha’, vol. 1)

“…the soul, after its separation from the body, will continue to progress until it attaineth the presence of God…”

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. 
(Baha'u'llah, Gleanings from the Writings of Baha'u'llah)

“…physical ailments, no matter how severe, cannot bring any change in the inherent condition of the soul”

Regarding your questions concerning the condition of the soul during illness. The passages in the "Gleanings" make it quite clear that physical ailments, no matter how severe, cannot bring any change in the inherent condition of the soul. As Bahá'u'lláh says: 'The spirit is permanent and steadfast in its station'. The veil or hindrance that interposes between soul and body during physical disease is sickness itself. Sickness reveals itself. Sickness reveals a lack of balance in human organism, an absence of equilibrium in the forces essential for the normal functioning of the human body. 
(From a letter written on behalf of Shoghi Effendi to an individual believer, March 8, 1936; Lights of Guidance)

We need to free our souls from the “bondage of self”

Deliver your souls, O people, from the bondage of self, and purify them from all attachment to anything besides Me. Remembrance of Me cleanseth all things from defilement, could ye but perceive it. 
(Baha’u’llah, ‘Gleanings from the Writings of Bahá'u'lláh’; The Compilation of Compilations, vol. II, The Importance of Prayer, Meditation, and the Devotional Attitude)

“…the human soul is exalted above all egress and regress”

In several of Our Tablets We have referred to this theme, and have set forth the various stages in the development of the soul. Verily I say, 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.... 
(Baha’u’llah, 'Gleanings from the Writings of Baha’u’llah'; Compilation ‘Reincarnation and the Nature and Progress of the Soul’, prepared by the Research Department of the Universal House of Justice)

The soul is God’s Sanctuary -- reason is God’s Throne

The soul is the Sanctuary of God; Reason is His Throne. 
(Words of ‘Abdu’l-Baha, recorded by Julia Grundy during her pilgrimage, ‘Ten Days in the Light of Acca’)

“The personality and activity of the body are due to the individuality of the soul.”

The personality and activity of the body are due to the individuality of the soul. Thus the soul is the cause of the life of the body, and the body, with all its organs, is but the vehicle of its expression. 
(‘Abdu’l-Baha, from a talk,  quoted by Lua Getsinger in her talk in San Francisco on December 17, 1911)(To see the transcript of the entire talk please visit Baha’i Talks, Messages and Articles)

The world of dream is a proof of the existence of the soul

… 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.... 
(Baha’u’llah, Gleanings from the Writings of Baha’u’llah; Compilation ‘Reincarnation and the Nature and Progress of the Soul’, prepared by the Research Department of the Universal House of Justice)

“..Mental faculties .. are in truth of the inherent properties of the soul ..”

Now concerning mental faculties, they are in truth of the inherent properties of the soul, even as the radiation of light is the essential property of the sun. (‘Abdu’l-Baha, ‘Tablet to August Forel’)

Government of one's self and soul

Moral life consists in the government of one's self. Immortality is government of a human soul by the Divine Will. 
(Words of ‘Abdu’l-Baha, recorded by Julia Grundy during her pilgrimage, ‘Ten Days in the Light of Acca’)

The “soul of man is a ray of light emanating from the Sun of the Word of God”

Therefore, since the reality or soul of man is a ray of light emanating from the Sun of the Word of God, it is capable of manifesting all the perfections of Being. It is then worthy to be the throne upon which may be established the manifestation of the Names, the Qualities and the Attributes of the Ancient Entity. Inasmuch as this entity is capable of expressing the great virtues of Being, and is the greatest and purest of all existing beings on earth, from its earliest rise in the human temple to its resurrection from the grave of the body, it can be likened to a mirror which reveals the seen and the unseen, which possesses the virtues of the world and of the Kingdom. 
('Abdu'l-Baha, from a talk, quoted by Lua Getsinger in her talk in San Francisco on December 17, 1911)(To see the transcript of the entire talk please visit Baha’i Talks, Messages and Articles)