The one from whom all beings arise, and by whom all this is pervaded — by worshipping that one through his own work, a human being attains perfection.
Explanation
Krishna is answering how one reaches perfection (siddhi) by devotion to one's own duty. He says the source of all beings, who pervades everything, can be worshipped through one's own work (svakarma). Work offered in this spirit becomes worship, not merely a livelihood. Commentators differ on whether 'that one' is the personal God or the all-pervading Brahman, but all agree that the offering of work is the key.