Did human wickedness move God to destroy mankind, or to promise never to do so again?

The two verses agree about human nature and differ about what God will do with it, and the difference is mercy. In 6:5 the evil is a reason for judgment. In 8:21 the Hebrew word ki, usually ‘for’, can also mean ‘though’, and many translations take it so: “Never again will I curse the ground because of man, even though every inclination of his heart is evil from his youth” (BSB). God is saying that the flood has not changed the human heart, and that he will not answer it again with a flood over the whole earth; he will bear with mankind instead. Calvin saw the point: if men ‘were to be dealt with according to their deserts, there would be a necessity for a daily deluge’.

Even if ki is read as ‘for’, the sense is the same: because evil is rooted in man from his youth, destroying the world again would never cure it. So God binds himself by covenant to keep the seasons going (8:22; 9:8–17), sets human justice to restrain violence (9:6), and goes on to his own remedy for sin, which unfolds from the call of Abraham. The flood shows what sin deserves; the promise after it shows the patience of God.

God’s answer to Noah’s offering

Keil and Delitzsch add that God’s resolve was also his answer to Noah’s sacrifice, which expressed man’s desire to stay in fellowship with God and to seek his favour.