Adam chose the tree of the knowledge of good and evil, and thereby took up independent ground.
In doing so he became a fully developed man.
He could command a knowledge; he could decide for himself; he could go on, or stop.
From then on he was wise.
But the consequence for him was death rather than life, because the choice he had made involved complicity with Satan, and brought him therefore under the Judgment of God.
That is why access to the Tree of Life had thereafter to be forbidden to him.