Q. What is Baptism? A. Baptism is a Sacrament which cleanses us from original sin, makes us Christians, children of God, and heirs of heaven.
Lesson Fourteen, No. 152, Baltimore Catechism
The gift of the sacrament of Baptism is the most valuable gift given by Catholic parents to their children. In Baptism a baby is cleansed of original sin, is made a child of God, and is made an heir of heaven (Baltimore Catechism). St. Thomas Aquinas said:
“Just as a man cannot live in the flesh unless he is born in the flesh, even so a man cannot have the spiritual life of grace unless he is born again spiritually. This regeneration is effected by Baptism: ‘Unless a man is born again of water and the Holy Spirit, he cannot enter into the kingdom of God’ (Jn 3:5).”
An unseen action takes place at the baptismal font as St. Maximilian Kolbe noted:
“The soul is regenerated in the sacred waters of baptism and thus becomes God’s child.”
A person becomes a child of God. This is very mysterious.
The Baltimore Catechism is quite thorough in explaining Baptism, the role of godparents, the promises of Baptism, etc: Baltimore Catechism on Baptism
The day we were carried to this mysterious font of life was a very happy day.