Bhagavān Kṛṣṇa continues the yajña teaching. In the previous shloka, he said that enjoying the gifts of the devatās without offering back is theft. Now he gives the positive and negative contrast in terms of food, because food is the most immediate example of receiving from Bhagavān’s order.

Yajña-śiṣṭa means what remains after yajña, what remains after offering. In daily life, this is prasāda — food or anything received after first acknowledging Bhagavān. When we offer food to Bhagavān and then partake of it, we are not merely eating. We are receiving with gratitude. The food becomes connected with reverence, humility, and karma-yoga.

The important idea is not that Bhagavān physically needs our food. Bhagavān is not hungry. The offering is for our transformation. Before offering, the food is looked upon as “mine, for my enjoyment.” After offering, it becomes “Bhagavān’s gift, given back to me as prasāda.” This change of attitude is the essence.

Those who live in this reverential way are called santaḥ — noble people, refined people. They are freed from sarva-kilbiṣaiḥ, all impurities or obstacles. Here kilbiṣa means pāpa, and pāpa is not merely a moral label. Anything that obstructs spiritual growth is pāpa. Anything that strengthens moha, selfishness, greed, entitlement, and forgetfulness of Bhagavān becomes an obstacle.

On the other hand, those who cook only for themselves — ātma-kāraṇāt — eat agham, sin. This does not condemn cooking itself or eating itself. The problem is the attitude: “This is only for me. I take, I enjoy, I do not offer, I do not thank, I do not share.” Such a life strengthens ego and moha.

Therefore, 3.13 teaches us to convert consumption into worship. Food and every karma-phala can be received as īśvara-prasāda. A reverential life is karma-yoga. A non-reverential life remains mere karma and binds.