Augustine of Hippo, On the Merits and Forgiveness of Sins, and on the Baptism of Infants I.16: How Death is by One and Life by One

Chapter 16 [XIII.]—How Death is by One and Life by One.

And from this we gather that we have derived from Adam, in whom we all have sinned, not all our actual sins, but only original sin; whereas from Christ, in whom we are all justified, we obtain the remission not merely of that original sin, but of the rest of our sins also, which we have added. Hence it runs: “Not as by the one that sinned, so also is the free gift.” For the judgment, certainly, from one sin, if it is not remitted—and that the original sin—is capable of drawing us into condemnation; whilst grace conducts us to justification from the remission of many sins,—that is to say, not simply from the original sin, but from all others also whatsoever.