पुरुषः प्रकृतिस्थो हि भुङ्क्ते प्रकृतिजान्गुणान्।
कारणं गुणसङ्गोऽस्य सदसद्योनिजन्मसु।।13.21।।
Because purusa (enjoyer, jiva) obtains in prakrti, (he) enjoys the
attributes born of prakrti. His attachment to the attributes is the cause for
births in higher and lower wombs.
Since the identification of the puruṣa, due to ignorance, with the modifications of
the gunas, is called samsara, it is clear that samsara does not belong to the purusa
who is atma. Prakrti cannot have samsara because it has no bhoktrtva. Only atma can
be a bhokta, because it alone is conscious; but being asanga and nirguna how does
atma become the bhokta with reference to the gunas of prakrti? It is only because of
identifying himself with them due to avidyā. The negation of samsara takes place when
this false identification resolves in the wake of knowledge.
Therefore, knowledge of the purusa is necessary and that is given in the following verse.
उपद्रष्टाऽनुमन्ता च भर्ता भोक्ता महेश्वरः।
परमात्मेति चाप्युक्तो देहेऽस्मिन्पुरुषः परः।।13.22।।
Here Sankara writes in his commentary as
प्रवृत्तान् स्वव्यापारेषु तत्साक्षिभूतः कदाचिदपि न निवारयति इति अनुमन्ता। - He is the anumanta because, when the body and organs are engaged in their own functions, He remains as a witness and never dissuades them.
It does not stand opposed to anything but is the great permitter, the one who does not resist at all. If the mind is restless dtma will light up the restlessness. When the mind is pleased, it will light up the pleased mind. It is not against any condition because its nature is luminosity like the Sun.
भरणं नाम देहेन्द्रियमनोबुद्धीनां संहतानां चैतन्यात्मपारार्थ्येन निमित्तभूतेन चैतन्याभासानां यत् स्वरूपधारणम्? तत् चैतन्यात्मकृतमेव इति भर्ता आत्मा इति उच्यते। - Bhartā is the one who sustains. The body, mind and senses exist and are conscious due to ātmā. The eyes function as instruments of sight and the ears as instruments of hearing because of ātmā. It gives existence not only to this body but to the entire prakrti. That prakrti, which is the cause of everything, is sustained by the purusa who is caitanya-ātmā. This consciousness is the sustainer of not only this body-mind-sense complex but of the entire creation.
Bhoktā means the one who finally enjoys everything, being the very svarupa of
the bhoktā. If ahamkāra is the bhoktā, purusha is the one that sustains that bhoktā.
Another meaning is, the one who devours everything, samharana-kartā. Everything is
dissolved in deep sleep, except purusha and also at the dissolution of the entire creation, everything is resolved into the purusha. All the names and forms are resolved into the prakrti-upadhi, which is rooted in the purusa. Therefore, purusa is called bhoktā, the devourer, samharana-kartā.
Hope this helps