In Colossians 2:11-12 Colossians 2:11-12  In whom also you are circumcised with the circumcision made without hands, in putting off the body of the sins of the flesh by the circumcision of Christ:
 Buried with him in baptism, wherein also you are risen with him through the faith of the operation of God, who has raised him from the dead.
American King James Version×, the apostle Paul compared repentance with circumcision. "In him [Christ] you were also circumcised, in the putting off of the sinful nature, not with a circumcision done by the hands of men but with the circumcision done by Christ, having been buried with him in baptism" (NIV). Paul also said, in Romans 2:29 Romans 2:29But he is a Jew, which is one inwardly; and circumcision is that of the heart, in the spirit, and not in the letter; whose praise is not of men, but of God.
American King James Version×, that circumcision is "of the heart."
Physical circumcision—the surgical removal of the male foreskin, or prepuce, which God commanded be done in infancy (Genesis 17:12 Genesis 17:12And he that is eight days old shall be circumcised among you, every man child in your generations, he that is born in the house, or bought with money of any stranger, which is not of your seed.
American King James Version×)—demonstrated for Abraham's descendants that they were in a covenant with God. Circumcision of the heart serves a similar purpose. When we change our way of thinking and behavior, we demonstrate our submission to God under the terms of a new covenant with Him.
Even though Paul likened baptism to the practice of physical circumcision, he did not mean that children should be baptized. Jesus did bless little children, but this was quite different from baptism (Mark 10:13-16 Mark 10:13-16  And they brought young children to him, that he should touch them: and his disciples rebuked those that brought them.
 But when Jesus saw it, he was much displeased, and said to them, Suffer the little children to come to me, and forbid them not: for of such is the kingdom of God.
 Truly I say to you, Whoever shall not receive the kingdom of God as a little child, he shall not enter therein.
 And he took them up in his arms, put his hands on them, and blessed them.
American King James Version×). Unlike physical circumcision, baptism must wait until we are mature enough to understand repentance and the magnitude of committing one's life to following God. The seriousness of baptism clearly makes it a decision for those who are mature.