What does it mean to say God “will not again curse the ground any more for man’s sake” (Gen 8:21)?

Let us be clear that he is quite specifically talking about the ground.He is not saying he will never again curse man. Rather, he is saying he will not give any further curse of the ground—of the sort given to Adam, then to Cain, and then to the whole of humanity in the Flood—i.e., the ground from which man lives. The remark, “I will never again destroy every living thing,” extends the promise of clemency. Moreover, the short poem of 8:22 I believe elaborates the meaning of “curse the ground,” by saying that the sunny days and the seasons of planting and harvest will continue; that would seem to undo Cain’s curse in particular, thus making it possible for all men to engage in farming again (though some, like Nebuchadnezzar, would be specifically cursed to engage in nothing but hunting and gathering). But we continue to live under Adam’s curse of the ground, which yields its fruits only after much toil; as Paul says, “the whole creation groaneth and travaileth in pain” (Rom 8:22).

Why did God say he would never again curse the ground (Gen 8:21)?

“Very well,” one might ask after reading the latter answer, “why not? After all, God just said that ‘the intent of man’s heart is evil from his youth’. Why not continue with the cursing and destroying of man?” The answer, I believe, is that the curse of the ground, i.e., the curse for Cain’s crime, for which God appeared to turn his face away from a whole line of people, has as it were “played out.” That line is destroyed; the world is reborn, and the reborn world is given a law and a covenant. It is as if God says, “See what you can make of this, ye hapless men with evil hearts; at least I will not utterly destroy you or curse the ground as I did Cain’s line, which was unusually wicked.” But since soon some (such as Canaan) were to be cursed (9:25-27), albeit by Noah, not by God—it seems God respected the curse. This makes it particularly clear that God means that all of humanity would not be cursed, at least, not as long as “the earth remains.” It is significant that God, in the end, will indeed destroy the earth again, as he utterly curses and destroys his enemies forever (see Rev 21:1 and its context). The time of clemency that began with Noah will not be forever.

God considers that “the imagination of man’s heart is evil from his youth” (Gen 8:21) when he announces he will never “smite any more every thing living”; but this is the same reasoning he used to destroy man (see Gen 6:5). What are we to make of this?

This is discussed above in connection to Gen 6:5, but let us return to the issue. Often such puzzles are solvable only if one assumes that the text is written with a surprising amount of subtlety. Fortunately, the text of the Bible bears up under such scrutiny; it really does have a surprising amount of subtlety. In this case, we are to compare what God says about “the imagination of man’s heart”—it is “evil from his youth”—to what he says about the antediluvians—“every imagination of the thoughts of [their] heart was only evil continually” (6:5); the three words I italicized here represent a significant difference. Man henceforth will, or at least should, be restrained by such practices as sacrifice, law, and awareness of God’s covenant and frightening sovereignty. He might still be “evil from his youth,” and so deserving of damnation; but at least his every thought will not be only evil continually. That is progress.