Badarayana, the author of Brahma Sutras, calls the being a knower, in contrast to its being knowledge itself. The soul acts. It is eternal and it not subject to birth and death. Birth and death and other changes happen to the body, not to the soul.
Badarayana seems to believe that he soul is atomic in
magnitude. Brahman and the soul are different like the sun and its light,
though the latter is very intimately present in the former. Badarayana says
that Brahman, as the very self of the soul, remains free from all pleasure and
pain while the soul experiences these profoundly.
Badarayana, at some places, says that the soul is an amsha
(part) of Brahman and sometimes that it is an abhasa (reflection) of Brahman.
He mentions, without his own comments, certain view like those of Asmarathya,
Audulomi and Kasakrtsna. Asmarathya holds that the soul is a part of Brahman.
Audulomi believes that at least in sleep, the soul is not different from
Brahman. Kasakrtsna thinks that Brahman and the soul are one and the same at
all times. Badarayana does not express his own judgement on these three
divergent views.
The soul is subject to all kinds of experiences for which it
alone is responsible. Brahman does not show any arbitrary partiality to anyone.
The soul is redeemed by the grace of God which can overrule even the momentum
of one’s own deeds. Action and renunciation find an equal advocacy in the
revealed scripture. Rather active service can go well with renunciation if the
two are judiciously blended.
A soul may have meditated on a personal God of its own
choice. In that case, it journeys after death along the lighted path of the
deva-yana (gods) on its way to liberation. It does not come back to the world
of mortals.
As regards the characteristics of the liberated soul,
Badarayana does not have a definite view. He says that the liberated soul is
pure consciousness (as held by Audulomi) and that it has an abundance of
glorious perfections (as maintained by Jaimini). Nevertheless, on one matter,
Badarayana is clear. Even the liberated soul does not have the power to create
or destroy the world. The power belongs to God and to none else.