rājanyo rakṣayā bhuvaḥ
vaiśyas tu vārtayā jīvec
chūdras tu dvija-sevayā
varteta — lives; brahmaṇā — by the Vedas; vipraḥ — the brāhmaṇa; rājanyaḥ — the member of the ruling class; rakṣayā — by protection; bhuvaḥ — of the earth; vaiśyaḥ — the vaiśya; tu — on the other hand; vārtayā — by trade; jīvet — lives; śūdraḥ — the śūdra; tu — and; dvija-sevayā — by serving the twice-born brāhmaṇas, kṣatriyas and vaiśyas.
The brāhmaṇa maintains his life by studying and teaching the Vedas, the member of the royal order by protecting the earth, the vaiśya by trade, and the śūdra by serving the higher, twice-born classes.
After glorifying karma, or work, Lord Kṛṣṇa now explains what He means by prescribed duties born of one’s nature. He was not referring to any whimsical activity, but rather to the religious duties prescribed in the varṇāśrama, or Vedic social system.