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’)