15.18 यस्मात् as, क्षरम् the perishable, अतीतः transcend, अहम् I, अक्षरात् than the imperishable, अपि also, च and, उत्तमः best, अतः therefore, अस्मि (I) am, लोके in the world, वेदे in the Vedas, च and, प्रथितः declared, पुरुषोत्तमः the Highest Purusha.

Commentary:
Purushottama is a wellknown name of the Lord. The name is ite appropriate as He is the supreme Purusha.Kshara The perishable -- the tree of Samsara.Akshara The imperishable -- the seed of the tree of Samsara.Because I excel the perishable (the tree of illusory Samsara) and am more excellent also than the imperishable (the seed of the tree of the illusory Samsara) and because I am thus superior to the perishable and the imperishable, I am proclaimed in the world and in the Vedas as the highest Purusha. Devotees know Me as such. Poets also describe Me as such.I am beyond all limitations. There is no trace of dualism in Me. Therefore, I am called by all and by the scriptures the highest Purusha.