यथैधांसि समिद्धोऽग्निर्भस्मसात्कुरुतेऽर्जुन। ज्ञानाग्निः सर्वकर्माणि भस्मसात्कुरुते तथा ॥

yathaidhānsi samiddho ’gnir bhasma-sāt kurute ’rjuna jñānāgniḥ sarva-karmāṇi bhasma-sāt kurute tathā

As the burning fire reduces fuel to ashes, O Arjuna, so doth the fire of wisdom reduce all actions to ashes.

In plain words: Krishna tells Arjuna that a blazing fire turns wood into ashes. In the same way, wisdom burns away the effects of all past actions.