Adam Clarke on Romans 5:16

And not as it was by one that sinned - That is, the judicial act that followed Adam's sin (the sentence of death pronounced upon him, and his expulsion from paradise) took its rise from his one offense alone, and terminated in condemnation; but the free gift of God in Christ takes its rise also from the many offenses which men, in a long course of life, have personally committed; and the object of this grace is to justify them freely, and bring them to eternal life.