"This individual soul is unbreakable and insoluble, and can be neither burned nor dried. He is everlasting, all-pervading, unchangeable, immovable and eternally the same. It is said that the soul is invisible, inconceivable, immutable, and unchangeable. Knowing this, you should not grieve for the body."
"The living entities are manifested and are divided into two classes, eternally conditioned and eternally liberated. Such living entities are innumerable, and they are considered fundamental parts of Krsna. Material energy is manifested into twenty-four divisions. The creation is effected by eternal time, and it is created and dissolved by external energy. This manifestation of the cosmic world repeatedly becomes visible and invisible.
...The living entity in his original position is pure spirit. He is just like an atomic particle of the Supreme Spirit. The conditioned living entity, however, is the marginal energy of the Lord; he tends to be in contact with both the material energy and the spiritual energy. In other words, the living entity is situated between the two energies of the Lord, and because he belongs to the superior energy of the Lord, he has a particle of independence. By proper use of that independence he comes under the direct order of Krsna. Thus he attains his normal condition in the pleasure-giving potency."
Bhaktivedanta Book Trust. HDG A.C. Bhaktivedanta Swami Srila Prabhupada.
"There is no other way out of this great ocean of Nescience except the unalloyed mercy of the Absolute Godhead. Living entity although superior in nature in comparison to the nature of matter, he is by association dependent and weaker than the material nature. The Absolute Godhead is the creator of all entities. He is the maintainer and deliverer of all entities. The unnumerable living entities are infinitesimals and Godhead is Infinite. The infinitesimal living entity is therefore subordinate to the Infinite and as such he is transcendentally the eternal servitor of the Absolute Godhead. The Supreme Spirit Godhead is the ultimate rest of all entities. This material world is a construction of the material energy and the material existence of the living entity is a sort of punishment just like a prisoner. The punishment is due to forgetfulness of Godhead by the living entity. And therefore there is no deliverance of the living entities from the clutches of Nescience save and except by the revival of his sense of Godhead. Those who have forgotten the relation of Godhead are only the prisoners of this Material world and those who have not forgotten Him are the liberated souls."
Srila Thakur Bhaktivinoda, "Back To Godhead, 1944 - 1960"
As explained in Bhagavad-gita, the jiva is prone to be sometimes in the realm of pure transcendence and sometimes under the influence of dull matter. This can be compared to the sand of a riverbank, which is sometimes immersed within water and other times exposed to the sunlight. The difference between the sand and the jivatma is that the jiva has the freedom to choose one condition or the other.
The jivas are infinitesimal and fixed in size, whereas the Vishnu-tattva expansions are infinite. Having expanded directly from the Supreme Lord, the jiva is qualitatively the same as God, but quantitatively infinitesimal. Jivas are individual beings with individual consciousness, but they are separated parts and parcels of the Supreme. Every living being is a fully unique individual spirit soul, and this individuality exists in us because we are qualitatively equal to the Supreme Being, who has His own individual identity.
Because the jiva is a living soul, he has the capacity to desire by his free will. While he is part of the Lord's superior nature, he is still influenced by ignorance due to his limited power. The Lord allows the living entity to fulfill his desires, even though they may bewilder him, yet the Lord is never responsible for the actions and reactions of a jiva's particular situation, whether desirable or undesirable. Because of his bewildered condition, the embodied soul identifies himself with the circumstantial material body, and consequently becomes subjected to the temporary misery and happiness of material life.
The soul is eternal and pure, and his eternal nature is to love and serve God. However, due to the jiva's free will and desire nature, he has a mistaken tendency to want to be God rather than serve God. It is this forgetfulness on the part of the individual spirit soul that causes him to fall down to this material world, where he can pretend to be the controller (something that he cannot do in the spiritual world). These material and spiritual desires form the basis of the divine and demoniac natures.
According to his association with the three modes of material nature, the living entity develops a particular type of body. In animal life, the material mode of ignorance is so prominent that there is very little chance of realizing Paramatma, who is also present within the heart of the animal; but in the human form of life, because of the developed consciousness (cetanam), one can be transferred from ignorance and passion to goodness by the results of his activities (kriya-phalatvena).
Although God is great and the living entity small, they are spiritual individuals, and therefore as soon as there is a reciprocal exchange by the living entity's free will, at once Krsna attracts the small living entity, thus freeing him from material bondage. When one attains perfect Krsna consciousness, he does not see anything but Krsna . The perfect devotee may see many movable and immovable objects, but at the same time he sees that the energy of Krsna is acting in everything. As soon as he remembers the energy of Krsna, the perfect devotee immediately remembers Krsna in His personal form, therefore all his observations lead him to see the Supreme Personality.