śukla — light; kṛṣṇe — and darkness; gatī — ways of passing; hi — certainly; ete — these two; jagataḥ — of the material world; śāśvate — of the Vedas; mate — in the opinion; ekayā — by one; yāti — goes; anāvṛttim — to no return; anyayā — by the other; āvartate — comes back; punaḥ — again.