In Augustine’s Enchiridion, chapter 46, which I am listening to in spare moments, he says this:
Here lies the necessity that each man should be born again, that he might be freed from the sin in which he was born. For the sins committed afterwards can be cured by penitence, as we see is the case after baptism.
This is, if I understand him, misleading at best.
Not that I want to minimize the significance of 1 John 1:9 (“If we confess our sins, he is faithful and just to forgive us our sins”). But to speak of new birth as being the way we are freed from pre-baptismal sin, and then penitence as the way we are freed from post-baptismal sin, is to create a two-phase dealing with sin that contradicts the way the death of Christ works—propitiating every sin of God’s elect, past, present, and future.
Here is the great evidence. Follow John’s reasoning in 1 John 2:1–2:
My little children, I am writing these things to you so that you may not sin. But if anyone does sin, we have an advocate with the Father, Jesus Christ the righteous. He is the propitiation for our sins, and not for ours only but also for the sins of the whole world.
In verse 1, John urges us not to commit any future (!) sins. But then he says if we do commit any future sins, we have an advocate in that case with the Father.
Then in verse 2, he bases the effectiveness of that advocacy on the finished, once for all, propitiating work of Christ. “He—this wonderful advocate—is the propitiation for our sins.”
Therefore, the very same propitiation that took the sting from our pre-baptismal sins also has taken the sting from our post-baptismal sins. My future sins are not dealt with any differently than the sins of my youth.
“The blood of Jesus his Son cleanses us from all sin” (1 John 1:7). All sin.