Baptism is the first of the sacraments and is the gateway which gives access to the other sacraments instituted by Jesus Christ. In the sacrament of Baptism the believer is united with Christ in His sacrificial death. The believer dies to sin and self and is resurrected with Christ to "new life", born again supernaturally into the family of God. "Baptism, Confirmation, and Eucharist constitute the 'sacraments of initiation' by which a believer receives the remission of original and personal sin, begins a new life in Christ and the Holy Spirit, and it incorporated into the Church, the Body of Christ." (CCC page 867).

The Regenerative Power of Christian Baptism which Images Christ

Christ's crucifixion and death Christ's Resurrection Christ's glorified new life
Our crucifixion with Christ and our death to sin and self into the waters of baptism arrow pointing right Our resurrection to new life through the power of the Holy Spirit i.e. "born again" or "born from above" in the image of Christ raised up through the water of baptism arrow pointing right Our final Resurrection and glorification at the end of time

Christian Baptism according to the practice of the early Church: "At dawn a prayer shall be offered over the water. Where there is no scarcity of water the stream shall flow through the baptismal font or pour into it from above; but if water is scarce, whether as a constant condition or on occasion, then use whatever water is available. Let them remove their clothing. Baptize first the children; and if they can speak for themselves, let them do so. Otherwise, let their parents or other relatives speak for them. Next, baptize the men, and last of all the women."
St. Hippolytus, Bishop of Rome, Apostolic Tradition: instruction on the sacrament of baptism [written circa AD 215]

When one receives the Sacrament of Baptism a supernatural sequence of events takes place which images the life of Christ. See Colossians  :9-14 and John 3:3-8; CCC # 628, 977-978.

  1. The believer dies to sin and therefore blameworthiness dies-we die to sin by renouncing sin and its power over us and being freed of its hold on our lives. We image Christ in this death to sin just as He died to free us from sin on the Cross.
  1. The believer is born "again" or "from above"; the Hebrew word onothan can mean either "again" or "from above" [see John chapter 3]. Our hearts are supernaturally "circumcised" and we are resurrection out of the waters of Baptism to a new life-no longer a child of Adam we become children in the family of God, imaging Christ's Resurrection from the tomb and fulfilling God's promise to make all things new through the New Covenant in Christ: Revelation 21:5-7, "Then the One sitting on the throne spoke. 'Look, I am making the whole of creation new. Write this, 'What I am saying is trustworthy and will come true.' Then he said to me, 'It has already happened. I am the Alpha and the Omega, the Beginning and the End. I will give water from the well of life free to anybody who is thirsty' and I will be his God and he will be my son."
  1. Baptism imparts the life of Christ's grace and, therefore, original sin and all personal sins are forgiven through the cleansing waters of Baptism in the regeneration and infusion of divine life by the power of God the Holy Spirit.

[However, concupiscence, the tendency to sin remained, see CCC# 978]

St. Ambrose, in his instruction to the newly baptized on the Sacrament of Baptism, taught, "The Lord who wanted his benefactions to endure, the serpent's plans to be turned to naught, and the harm done to be put right, delivered a sentence on mankind: 'You are dust, and to dust you shall return' (Genesis 3:19), and made man subject to death."; Then, as St. Ambrose continues, God in His mercy provided a remedy: "The remedy was given him: man would die and rise again... You ask me how? Answering his own question St. Ambrose informed the newly Baptized, "Pay attention! So that in this world too the devil's snare would be broken, a rite was instituted whereby man would die, being alive, and rise again, being alive... rough immersion in water the sentence is blotted out: 'You are dust and to dust you shall return.'" St. Ambrose writing on the Sacrament of Baptism, De Sacramentis, II,6

Baptism is not merely a symbolic death and rebirth but is a genuine participation in Christ's saving mission—death, burial, and Resurrection as figured in water immersion [death and burial], and coming "up" out of the water [Resurrection]. The regenerative waters of baptism yield a transformation and rebirth. In Scripture a "sign" points beyond the event to a more significant event. Baptism is a sign or symbol only in the sense that it is symbolic of the greater supernatural reality of the sacrament which shows in a visible form God's action to perform what the physical event signifies-resurrection to new life in Christ. The sinner is immersed in water and is thus "buried" with Christ [Colossians 2:12], with whom the Christian is also raised up through the water to resurrection [Romans 8:11] as a "new creation-infused with "divine life"[2 Peter 1:3-4; 2 Corinthians 5:17], and as a member of God's family and at one with the Body of Christ animated by the one Spirit [1 Corinthians 12:13; Ephesians 4:4ff]. However, the Christian's resurrection will not be complete or final until the End of Time [1 Corinthians 15:12]. Paul assures us that Christians having been freed from sin are literally freed from the power of sin over their lives because God's grace is more powerful that the power of sin. [Also see Galatians 3:27-28; 1 Corinthians 12:12-13; Colossians 2:9-14, 3:10; Ephesians 4:4-6].