In plain words
Naraka-asura. He was a demon. Because he had come under tamoguṇa, he was named Naraka. He who travels on the downward course, he is Naraka. He who travels on the upward course is nara. We must make the flame blaze upward. We must make the flame of our life grow upward. That is, with a steady citta we must develop the noblest feelings and holy deeds. Through unholy deeds, through loathsome deeds, our vision goes downward. Even God does not try to destroy the wicked who take part in such evil deeds. Such a man, too, God will not consent to punish. Is it kindness towards him? Prema? Or grace? No, no. God will not consent even to go near him. So He laid a kind of master plan to wear down his strength and powers little by little. That Narakāsura's bodily strength was very great. His strength of mind too was very great. Taking his strength of body and of mind into account, He resolved to wear it down little by little. What is the root cause of all this strength of body and mind wasting away? Anger itself is its root cause. However strong a man may be, when he goes on giving way to anger beyond all measure, his bodily strength dwindles away. Let a man grow angry just once, and all the strength of three months' eating wastes away. Every time, Kṛṣṇa would go to battle against Narakāsura, come back again as though Naraka were chasing Him, and turn back once more: this is what Kṛṣṇa kept doing. Kṛṣṇa resolved to stir up his anger and destroy his bodily strength completely. When in this way Naraka had wholly destroyed all his strength by his own anger and had grown weak, even then Kṛṣṇa did not kill him Himself; since by the dharma of Prakṛti one who has tormented women must be killed by a woman alone, He took Satyabhāmā along and had him killed by her. For destruction of this kind God lays certain master plans. He lays a master plan for protection too. For everything there is a master plan. For He Himself is master. So: ‘master the mind be a master mind.’ Being master Himself, He lived on with a master mind.