Beings come into being from food; food comes from rain; rain comes from sacrifice; and sacrifice arises from action.
Explanation
Krishna is explaining to Arjuna why selfless action offered as sacrifice (yajña) matters, continuing from the previous verse. He describes a chain of dependence: living beings rely on food, food on rain, rain on sacrifice, and sacrifice on action (karma). The point is that human work is woven into the larger order of the world. Traditions differ on whether 'sacrifice' here means Vedic ritual specifically or any duty done as an offering, and the next verse continues the chain.