While we come to Atman, we should also understand two terms that are used in Hindu religious literature profusely. Both come from the word Atman. When it connects to a living body, we call it jIvAtmA , when it refers to the origin it is paramAtmA. jIva in Sanskrit means one that "lives". jIvAtmA is the signature of a living object, or more particularly the perceived manifestation of Atman in the living object. By definition, the Atman carries the cognitive element in the manifested universe and so, the jIvAtmA as conceived becomes the cognitive element in the living object.
In the western literature, jIvAtmA is conceived as the soul of the living object and life's pleasure and pain are mapped on to it. The idea is that soul can suffer because of our accumulated "sins" and the soul can be punished for its misdoings either in this life or in later lives, or in a "day of judgment" as a faith might suggest. In the eastern literature, the jIvAtmA does get tarnished through its embodiment and assumes a sequence of new bodies in a process of constant purification. Unfortunately the new embodiment might bring in further impurity and hence path to liberation becomes an onerous process. Prescriptions are made for good conduct and righteous living in order to get out of the "life cycle" faster.
What's this "life cycle?" The original Atman that caused the universe is labeled "supreme," called parama in Sanskrit. So we have the origin of the universe caused by paramAtmA, which gives rise to multiple jIvAtmA in a figurative manner (see below). Each jIvAtmA remains capable of creating new life in order to get embodied in casings that are limited because of the bodily manifestation. The process can continue till dissolved by a cataclysm of some kind in course of time. The origin of such a cataclysm is the part of a larger design to deal with the larger cycle of evolution. The measurement of time in the universe begins with the first manifestation and ends with the dissolution of the universe. After dissolution the universe can be recreated by paramAtmA through the same conceived design as before, or in an altered design as suitable. paramAtmA is endowed with infinite abilities and hence may be considered as the "Lord" of the universe. Terms like "Is'vara" and "God" are used to comprehend the concept of paramAtmA. The life cycle of the jIvAtmA is then its cycle of journey in the universe until it can merge itself back with the paramAtmA. Concept of such a life cycle becomes a necessity to appreciate the pains and pleasures in life.
In the wordy description above, one subtle philosophical point got hidden. Since Atman is infinite, and the paramatmA is infinite, there is no reason why the jIvAtmA would not be infinite. Mathematically it must be, except it appears finite because of its containment in the body, and because of its new assumed role of operating the body. We have said before that the jIvAtmA accepts the stains of the impurities in the body and encases itself in a body that has likely sustained the earlier stains. It's hypothesized that the human desires driven by ego are the principals among the stains and the new body may adopt a path of restraint to cleanse itself from the past stains.
The theory of jIvAtmA and paramAtmA allows a beautiful short-cut for one's blissful existence with the mortal body. This is done by the realization that jIvAtmA and paramAtmA are indeed non-different. In this process the living object declares its divinity right away and explores the sameness of the living force in the entire universe. This exploration can lead to ecstasy and the success brings joyful self-realization. Identifying one’s own self with everything else in the universe is the realization of yoga. Such realization is the element of Ananda that we have discussed before.
The theory of pain and pleasure in life brings us to the philosophy of sAnkhya and the declaration of the divinity of life everywhere brings us to the philosophy of yoga. We will discuss these as we go along.
Let Sai's blessings be with all.
Happy New Year