Kṛṣṇa gives an exception to the rule of work. He says that for a person who finds all their pleasure and satisfaction within their own soul, and who is fully self-realized, there is no prescribed duty left to perform. They have reached the goal. The purpose of work and social duty is to purify the mind and detach it from matter. Once a person is ‘ātmany eva ca santuṣṭas’, or fully satisfied in the self, the ‘medicine’ of prescribed duty is no longer needed because the ‘disease’ of material desire is cured. However, this is a very high stage of perfection. Until one is completely free from even the slightest material desire, they must continue to work. Kṛṣṇa is defining the finish line, but He is also subtly reminding Arjuna that he hasn’t crossed it yet. As long as Arjuna is feeling grief and attachment, he still needs the path of work for his purification.