Video from Desiring God
Look at the Book: The Sign of Circumcision and Baptism: Colossians 2:11–12, Part 1
Is baptism the New Covenant equivalent of circumcision?
"Circumcision was the physical sign of the covenant God made with Abraham. Although the initial covenant was made in Genesis 15, circumcision wasn’t commanded until Genesis 17 – at least 13 years later, after Ishmael was born. At that time, God changed Abram’s name from Abram (“exalted father”) to Abraham (“father of a multitude”), a name that anticipated the fulfillment of God’s promise. The covenant was made with Abraham and later to Isaac and Jacob and to all their descendants.
Baptism is, in some sense, the sign of the New Covenant God makes with His Church. Jesus commanded baptism in the Great Commission: “Go therefore and make disciples of all nations, baptizing them in the name of the Father and of the Son and of the Holy Spirit” (Matthew 28:19). Baptism is the outward sign of an inward change. It represents rebirth in Christ.
Many Reformed traditions have made a very close parallel between circumcision and baptism and have used the Old Testament teaching on circumcision to justify the baptism of infants. The argument goes like this: since infants born into the Old Testament Jewish community were circumcised, infants born into the New Testament church community should be baptized.
While there are parallels between baptism and circumcision, they symbolize two very different covenants. The Old Covenant had a physical means of entrance: one was born to Jewish parents or bought as a servant into a Jewish household (Genesis 17:10-13). One’s spiritual life was unconnected to the sign of circumcision. Every male was circumcised, whether he showed any devotion to God or not. However, even in the Old Testament, there was recognition that physical circumcision was not enough. Moses commanded the Israelites in Deuteronomy 10:16 to circumcise their hearts, and even promised that God would do the circumcising (Deuteronomy 30:6). Jeremiah also preached the need for a circumcision of the heart (Jeremiah 4:4).
In contrast, the New Covenant has a spiritual means of entrance: one must believe and be saved (Acts 16:31). Therefore, one’s spiritual life is closely connected to the sign of baptism. If baptism indicates an entrance into the New Covenant, then only those devoted to God and trusting in Jesus should be baptized.
True circumcision, as Paul preaches in Romans 2:29, is that of the heart, and it is accomplished by the Spirit. In other words, a person today enters a covenant relationship with God not based on a physical act but on the Spirit’s work in the heart.
Colossians 2:11-12 refers to this type of spiritual circumcision: “In him 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 and raised with him through your faith in the power of God, who raised him from the dead.” This circumcision does not involve the cutting of the body; it is a cutting away of our old nature. It is a spiritual act and refers to nothing less than salvation, effected by the Holy Spirit. Baptism, mentioned in verse 12, does not replace circumcision; it follows circumcision—and it is clearly a spiritual circumcision that is meant. Baptism, therefore, is a sign of inward, spiritual “circumcision.”
This passage also specifies that the new life, represented by baptism, comes “through your faith.” This implies that the one being baptized has the ability to exercise faith. Since infants are not capable of exercising faith, they should not be candidates for baptism.
Someone born (physically) under the Old Covenant received the sign of that covenant (circumcision); likewise, someone born (spiritually) under the New Covenant (“born again,” John 3:3) receives the sign of that covenant (baptism)." from the article: Is baptism the New Covenant equivalent of circumcision?