Before jumping into baptism, it’s important to understand Original Sin and the biblical support for this Catholic teaching. In the beginning, man (Adam and Eve) existed in a state of holiness, called Original Justice, but he lost this grace upon disobeying God’s command not to eat from the tree of knowledge of good and evil. The consequences of their personal sin, physical death and loss of supernatural life, were passed on to future generations (read Rom 5:12-21 and 1 Cor 15:20-22). Adam and Eve, before the Fall, were inclined to God’s will. After the Fall, they were, and we as their descendants are, inclined to sin (concupiscence). To remedy this problem, God sent His Son, Jesus, the very Word made flesh, into the world and He willingly sacrificed Himself for mankind. This was and is a free gift we certainly do not deserve. We enter into this free gift by way of God’s grace and our response to His grace, which is faith. But this isn’t the end of the story.
Original Sin is the primary reason for baptism. What Adam and Eve lost (unity with God through Original Justice), Christ restored, though we continue to suffer the consequences in this life. Through baptism, we join Christ’s body so that we can be restored to unity with God (Rom 6:3-5). This is why age doesn’t matter. Jesus said we are born anew (or born again) by “water and Spirit,” which is baptism (Jn 3:3-7) and Paul adds in Titus 3, “…by the washing of regeneration” (again baptism; regeneration meaning born again). Baptism washes away Original Sin and personal sin (infants and children do not commit personal sin of course) and restores grace (supernatural life) to the soul. The effects of Original Sin, natural death and inclination toward sin, are still present. But the gift of sanctifying grace through baptism works within the soul, so that we are able to cooperate with God’s will. Although we are still inclined to evil deeds, we are now capable of engaging in spiritual battle and turning away from our personal sins. If you’re wondering why God went to all the trouble to save us rather than simply waving a magic wand to forgive us our sins, we need to simply look at human nature.
When people do something wrong and are forgiven but never corrected, they continue in the same behavior. We have an entire legal system built upon this very premise. We need only look ourselves and the Jews in the Old Testament. Although God could simply forgive us every time we sin, we would never learn to repent and turn away from our sins. Jesus was tortured and died on the cross as an example of supreme and perfect love, which we are called to imitate (1 Thes 1:6, 1 Cor 11:1). Besides being an example of perfect love, Jesus died as a sacrifice for all mankind. Adam, a finite man, transgressed against an infinite God; the dividing wall between man and God was built. To repair the damage caused by Adam, Jesus, who is both God and man sacrificed himself; the dividing wall was torn down. In other words, “Jesus had to be human so that he could make atonement for the sins of the human race. He had to be God so that the atonement would have infinite value, and thus make reparation to an infinite God.” Paragraphs 396 to 412 of the Catechism and Romans chapter 5 give a detailed treatment of Original Sin. Read Romans 6:1-14 on the importance of baptism.
A Protestant interlocutor might object to baptism by saying it’s a work and, therefore, not necessary for salvation. But let’s briefly examine Titus 3:5-8, which states, “[Jesus] saved us, not because of deeds done by us in righteousness, but in virtue of his own mercy, by the washing of regeneration and renewal in the Holy Spirit, which he poured out upon us richly through Jesus Christ our Savior, so that we might be justified by his grace and become heirs in hope of eternal life. The saying is sure.” First, the washing of regeneration and renewal by the Holy Spirit is baptism. Second, notice that Paul states Jesus saved us “not because of deeds done in righteousness” but by his mercy in the “washing of regeneration.” Therefore, baptism is not a deed done in righteousness, but “an appeal to God for a clear conscience” (1 Pet 3:21). If you are not righteous before baptism, then baptism cannot be a deed you do in righteousness. Third, Paul explains that through the washing of regeneration, we are justified by God’s grace. Therefore, baptism justifies by appealing to God and washing away our sins. Baptism is not a good deed done in righteousness, but an appeal to God, who then does the work of washing away our sins. Faith without baptism does not save except in extraordinary circumstances. Now, we are left with one more question. What happens when we commit mortal sin after baptism?
 Frank Chacon and Jim Burnham, Beginning Apologetics 2, Farmington, NM: San Juan Catholic Seminars, Pg. 7.