4.15 Actions of the kind described above were performed even by the aspirants of old for liberation, who have become free from evil after knowing Me in this way. Therefore, after having got rid of the sins by knowledge of Me in the aforesaid way, perform actions in the same way as they were performed by those ancients like Vivasvan, Manu etc., in olden times, in the way in which their performance was taught by Me even then. I shall declare it again in what follows.

Sri Krsna stresses the difficulty of undertaking the type of Karma that is going to be taught now.