अन्नाद्भवन्ति भूतानि पर्जन्यादन्नसम्भवः। यज्ञाद्भवति पर्जन्यो यज्ञः कर्मसमुद्भवः ॥

annād bhavanti bhūtāni parjanyād anna-sambhavaḥ yajñād bhavati parjanyo yajñaḥ karma-samudbhavaḥ

From food creatures become; from rain is the production of food; rain proceedeth from sacrifice; sacrifice ariseth out of action.

In plain words: Krishna describes a cycle: living beings come from food, food comes from rain, rain comes from sacrifice, and sacrifice comes from action.