But there is another, the highest Purusha, called the Supreme Self, the imperishable Lord, who enters the three worlds and sustains them.
Explanation
Krishna has just named two kinds of purusha (person or being): the perishable (kṣara), meaning all created beings, and the unchanging (akṣara), called the "steady" one. Here he points to a third, higher purusha, the Supreme Self (paramātman), who is beyond both. This Lord pervades the three worlds and upholds them without ever decaying. Traditions differ on how this Supreme Self relates to the individual self: non-dualist readings stress their ultimate identity, while theistic ones stress a real distinction.