First, recall that his name is Adam, taken directly from the Hebrew אֲדָמָה, adamah, or ground. He is introduced as the “generation” of the earth, or dust; and he is destined to be a tiller of the ground. If the text at Gen 2:15, even before the Fall his job was “to dress [the Garden] and to keep it.” And yet, he rebelled, asserting his independence of God, and worse, failed to take responsibility for his own sin, failing to seek forgiveness. Hence it was only natural that God would respect his decision, causing him to fall back on his own natural resources. Adam, it seems to me, probably did not understand the nature of the evil Tree, that it would give him knowledge in the sense of first-hand experience of the blessings and curses of life without God, a knowledge God did not wish on him. But he chose the tree that gave such knowledge. Since he is of the earth, his punishment is to wear himself out by tilling the earth, an earth that gives up its fruits only with toil and sweat, quite unlike the Garden.