In plain words
Naraka had taken women captive and tormented them in many ways. So Kṛṣṇa resolved to have him killed by a woman, took Satyabhāmā along with Him, and went to war against him. Sixteen thousand princesses, women of supreme devotion, had fallen into that demon's hands and were suffering the torments of hell. Kṛṣṇa granted them freedom. Marking this, Tyāgarāja sang thus in praise of Kṛṣṇa's divine deeds:
You are beyond the reach of speech; is it in the power even of Brahmā and the gods to praise Your deeds! O Kṛṣṇa! I have been waiting; hear my plea and save me. The guru's son whom Death had carried off, You brought back and restored; You crushed the pride of Kāḷīya; You freed Vasudeva and Devakī from prison; when Draupadī, a woman alone, cried out, ‘Ah, Kṛṣṇa! Kṛṣṇa!’, You saved her; well done, well done! You guarded the Pāṇḍavas. You ended Kucela's distress; You took away the crookedness of misshapen Kubjā; You saved the sixteen thousand jewels among women …
What does the slaying of Narakāsura mean? Narakāsura is the asura dwelling in nara, in men. Nara means one who is the embodiment of the Ātma. Into such a man an asura full of bad qualities and evil thoughts has entered. Such a one keeps company only with the wicked and not with the truthful; he does not try to reach the Paramātma. Through the fruit of the sins of birth after birth, his mind strays onto a wrong path in this way.
Man today fancies that he is highly learned. But what he has truly learned is no learning at all; it is mere ignorance. How can that be learning which does not teach good qualities and right standards? Rāvaṇa too learned the arts that Rāma learned.