The Veda speaks of the ‘Sacrificer’ going to heaven after death; the body perishes after death; hence the Entity that is spoken of as ‘proceeding to Heaven’ must be something other than perishable body. This entity is आत्मा or soul. If there is no such entity, then the Veda has made an absurd statement & this strikes at the reliability of Veda; and hence at the very root of Vedic philosophy.
This soul (Read आत्मा) is something different from the Body, the Sense-organs and Buddhi; it is eternal, imperishable; it is real doer of the actions, agent of acts, and the experiencer of their results and reactions. It is also all pervading. That is the notion of ‘I’ which is all the notion that we have of soul, which is of the nature of pure Consciousness, and is not qualified by any limitations of time and place. It is soul that passes through the experiences of pleasure, pain etc; and yet it never renounces its own character of Consciousness; it forms the constant factor in all those variable and varying experiences. The soul experiences the reactions of all acts. The idea that ‘there is no soul’ can be kept aside by the universally recognized notion of ‘I’.
The question arises- “If words are incapable of bringing about the cognition of the soul, by what means is it cognized?”
The answer given by the scriptures is that it is ‘illumined’ – made cognizable-‘by itself’ and what is meant by ‘self-luminosity’ is that one Soul cannot be directly cognized, by another Soul,-it is cognized by another only through Inference, drawn from the perception of such activities in the other personality as have been found, in one’s own Soul, to be invariably concomitant with the Soul. It is clear, therefore, that for such person, his own Soul is Self-luminous, Self-cognized; but for other persons, it is cognized through Inference.
Connection of one soul with one body at a time is being determined by the past Karma of the soul which is always equipped with a body that is capable of bringing about the experiences resulting from that past karma of the personality.This continuous connection of the Body with the soul is exactly like the continuous connection of the body with space or time, which latter also are omnipresent. The soul being itself immaterial, cannot move from place to place; when therefore man moves from one place to another, his soul would be left behind; and the body would become soul-less and hence in-animate. But soul is omnipresent, wherever body goes, it finds itself ensouled by the soul. If soul was not omnipresent, it would be either atomic in size or of the size of the body. It cannot be former; as if it were so, the person could be conscious of only those sensations that would appear in that small part of the body which would be occupied by atomic soul; this is absurd. Later would raise gratuitous assumptions. When we talk about soul as omnipresent, one soul cannot serve the purpose for all personalities, as that would mean that one and the same soul undergoes the experiences of all persons. The soul therefore must be regarded as many and existing simultaneously. Being immaterial, they would not come in each other’s way. In fact, it is on account of this immateriality and consequent indivisibility of souls and their omnipresence, and all being of the same pure Consciousness, Upanishad-texts have spoken of all souls as one.
– Kumarila Bhatta in Tantra Vartika