The sacrament of Baptism is not merely a symbolic ritual, externally reflecting the interior faith of the recipient (or, in the case of infants, the recipient’s parents and godparents).  In baptism, we are truly born anew, “of water and the Spirit” (John 3:5).  However, a new birth implies a first birth, namely, our birth “into Adam,” into the state of original sin (see 1 Corinthians 15).  This is the meaning of St. Paul when he speaks of our “old nature,” which must be cast off and replaced by a “new nature.”  And he is very clear about what this new nature is like:

“Christ is all, and in all.”  ~ Colossians 3:11

Therefore, Baptism is a sacrament of conversion. It has two effects: forgiveness of original (and, in adults, personal) sin and divine adoption as a child of God (which makes us members of the Church).  Through baptism, we pass from the shadows of death and sin to the life of grace, by which we “put on Christ” (Galatians 3:27) and are made “partakers of the divine nature” (2 Peter 1:4).  This mystery was foreshadowed by the great deliverance of the people of Israel from Egypt. Just as Israel was freed from Egypt by passing through the waters of the Red Sea, so too the Christian passes through the waters of baptism and becomes a “wayfarer” toward his or her heavenly homeland (see 1 Corinthians 10:1–4).  

Thus, through Baptism, we are not merely called children of God; we truly are “Christified”:

“For as many of you as were baptized into Christ have put on Christ.” ~ Galatians 3:27

This new birth and new nature will be the source of all the grace-filled deeds that we perform through all our life.  All the other sacraments will serve in helping us to maintain, renew, and deepen this life, from baptism until the eternal dawn of heavenly glory.

{excerpt  taken from Ascencion Press "Journey thru the Catechism"}