John Calvin Commentary Romans 5:16

"And not as through one that sinned, [so] is the gift: for the judgment [came] of one unto condemnation, but the free gift [came] of many trespasses unto justification." — Romans 5:16 (ASV)

This is especially an explanation of what he had said before—that by one offense guilt resulted in the condemnation of us all, but that grace, or rather the gratuitous gift, is efficacious for our justification from many offenses. It is indeed an expansion of what the last verse contains; for he had not until now expressed how or in what respect Christ excelled Adam.

This difference being settled, it appears evident that the opinion of those who have taught that we recover nothing else by Christ but freedom from original sin, or the corruption derived from Adam, is impious. Observe also that these many offenses, from which he affirms we are freed through Christ, are not to be understood only as those which everyone must have committed before baptism, but also as those by which the saints daily contract new guilt, and on account of which they would be justly exposed to condemnation if they were not continually relieved by this grace.

He sets gift in opposition to judgment: by the latter, he means strict justice; by the former, gratuitous pardon. From strict justice comes condemnation; from pardon, absolution. Or, to put it another way, if God were to deal with us according to justice, we would all be undone; but he justifies us freely in Christ.