I think you will find the answer to your question in Rom ch.7. We are a battleground. The Spirit and the Flesh are at war in our members constantly. Through baptism, we receive the grace to overcome sin, but this is only the beginning of the victory. the war must be fought until we are called home.
Baptism does forgive all sins, those committed, and original sin. After baptism, the soul is entirely pure before God. this is why, in the olden days, people used to wait until death’s door to become baptized.
No, I don’t think that is it. I think it is more like:
- Assume being born again happens at baptism
- catholics who are baptized as infants are supposedly “born-again”
- Scripture shows us that “born-again” people act differently (flee from sin)
- Many Catholics do not act according to what the Bible says “born-again” people should
- Are these people really “born again”?