Here’s my understanding. I’d appreciate comment from those who actually know what they’re talking about; this has been running around in my head for a while and I could use some help.
Original sin is the state of existence in which we are deprived of the original union with God that Adam had. When Adam sinned, he broke that union and so was unable to pass it on to us. This hasn’t changed.
Passover remembered the redemption of Israel from slavery to Egypt, and was symbolic of the coming Messiah who would redeem the world from slavery to sin. The sacrifice of the paschal lamb did not make redemption real: it was a symbol. As the true Paschal Lamb, Christ’s sacrifice makes the redemption real: the price has been paid to buy us out of slavery to sin, and we are actually brought into a family relationship with God. The Jews believe that at the Passover celebration they are mystically present at the first Passover in Egypt, and the Church teaches that at the celebration of the Eucharist we are mystically present at Calvary. Christ’s sacrifice is a more perfect fulfillment.
In the same way, the ritual baths of the OT were symbolic of the cleansing from sin. Baptism in the Mikveh did not actually wash away sin, but the baptism of Jesus does. I believe this is what Jesus meant when he said “If you knew to whom you were speaking, you would ask and He would give you living water”. The phrase “living water” was a term of art that referred to the waters of the mikveh, which were to be provided to the bath directly from the source, without being handled, and thus directly from God. When Jesus claimed to be able to provide “living water”, He was making a claim to deity.
Regarding the Cross, I find verses like Romans 6:6 (crucified with him…that we might no longer be in slavery to sin), which seems to refer to our being freed from slavery to sin.
Regarding Baptism, I find ones like John 3:5, Acts 2:38, Acts 22:16, 1 Corinthians 6:11, 1 Corinthians 12:13, 1 Peter 3:21, Ephesians 5:25-27, Colossians 2:12-13, and Titus 3:5, which seem to emphasize our being buried with Christ and brought back to life as part of His body, with our sins washed away.
As Passover and the mikveh symbolized the distinct graces of redemption and cleansing, so the Eucharist and Baptism actually bring them into effect. The two sacraments do different, but related, things.
There is a real benefit to infant baptism. Read the Catechism, paragraphs 1250-1252 and 1262-1274. As circumcision created a physical sign that one was part of God’s covenant, so Baptism creates a spiritual sign of belonging to Christ. It cleanses the child from the stain of original sin, thus bringing him into a special and intimate relationship with God that he otherwise would not have. It enables him to believe in God, hope for Him and to love Him; provides the power to live and act under the prompting of the Holy Spirit; and allows them to grow in goodness. It makes him a member of the Body of Christ.
Gee, the more I think about this the more exited I get!