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)