It is desire, it is anger, born of the quality of rajas. It is all-consuming and greatly sinful. Know this to be the enemy here in the world.
Explanation
Arjuna has just asked what drives a person to do wrong even against their will. Krishna answers that the force is desire (kāma), which also shows itself as anger (krodha), and which arises from rajas, the guna of restless energy and craving. He calls it a 'great devourer' (mahāśana), meaning it is never satisfied. Traditions differ on whether desire and anger are two forces or one force in two forms, but all agree that Krishna names it as the enemy.