What is action and what is inaction: even the wise, the discerning, are deluded here, in this matter. So I shall declare to you action and inaction, knowing which you will be freed from what is inauspicious, from transmigration. You should not think 'action is the well-known bodily activity and the rest, and inaction is its non-doing, sitting silent; what is there to be understood in that?' Why is it said?

What is the nature of the action a seeker of liberation must perform, and what is inaction? Action done with no eye to its fruit, in the form of the worship of the Lord, is called 'inaction', that is, the knowledge of the doer, the self, as it truly is. What is the nature of the action to be performed, and of the knowledge included within it? On both points even poets, even the learned, are deluded and do not know it as it truly is. So I shall declare to you that action which has knowledge included within it, knowing and performing which you will be freed from the inauspicious, from the bondage of transmigration. For the knowledge of the action to be done is itself the fruit of the performance. Why is this hard to know? To this the Lord speaks.

This is a brief sub-gloss. For a fuller reading of this verse, see Madhusūdana, Śaṅkara, or Rāmānuja above.

It was said, 'do action'. To speak rightly of how hard that action is to know, Krishna says, with 'what is action, what is non-action'.