Knowing this, action was done even by the ancients, the seekers of liberation who have passed away. Therefore do you too do that very action, and do not sit silent, nor renounce; you should do it because it was carried out even by the ancients. If you do not know the Self, then do it for the purification of the self; and if you do know the truth, then do it for the holding-together of the world. It was done by the ancients, Janaka and the rest, in a still earlier time, not done newly now. Now, if action is to be done, I do it on Your word alone; why is it specified that it was 'done by the ancients in a still earlier time' (Gītā 4.15)? Because there is a great unevenness in action. How?

Knowing Me thus, even the seekers of liberation of old, freed of sin, did the action of the character described. Therefore you too, your sin shaken off by the knowledge of Me of the kind described, do that very action, ancient, more ancient still, of the form about to be told, which was done of old by Vivasvat, Manu, and the rest, and was declared by Me at that very time. The Lord states how hard the action about to be told is to know.

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

There is also the example of conduct, of doing action with this knowledge, Krishna says, with 'thus'. 'Action done in still earlier times' means that which existed before; that is the sense.