In theological discussion presuppositions must always be accounted for. It is foolishness to ignore presuppositions. This is why two people can read the same text and come away with two opposing interpretations. As a Covenant theologian, I do not for a second hide the fact that my presupposition is this: Covenant is the framework upon which everything in Scripture attaches. Everything which God has revealed, He has revealed through the grid of covenant. This seems like a fair conclusion. I do not believe this to be an artificial paradigm imposed upon Scripture. If we follow the Reformation principle of letting Scripture be its own interpreter, it seems clear that covenant is the underlying framework upon which all revelation is affixed.
Since the Baptist does not view covenant this way, he differs from the Reformed theologian when it comes to the administration of the covenant of grace. At the heart of the baptistic argument against infant baptism is the denial that baptism has replaced circumcision as the sacrament of entry into covenant with God. Reformed theology teaches that baptism is the New Testament version of circumcision. If this concept were clearly grasped, much confusion would be cleared away.
Having prefaced all that, let us now look at some Scriptural evidence for the contention that baptism is, in fact, Christian circumcision.
In Colossians 2:11, Paul tells us, “in Him you were also circumcised with the circumcision done by Christ." Before we proceed, it is crucial to remember Paul’s constant invective against those who insist that circumcision is necessary for Christians. It should be obvious then that whatever Paul is referring to here, he does not mean physical circumcision. Let’s let Paul explain himself. How does he say we were circumcised by Christ? He says, “having been buried with him in baptism and raised with him through your faith.” The first word of verse 12 (συνταφεντες), is a participle described the circumstances in which believers are circumcised. In other words, Paul is saying that we are circumcised with a spiritual circumcision (made without hands) with the circumcision of Christ and this is done by being baptized. It is common (based on Romans 6) to use burial as an illustration of baptism. Notice here though, that Paul uses burial as an illustration of circumcision. He says, “You were circumcised by having been buried…”
Therefore Paul concludes that in the New covenant, our baptism is our circumcision. It identifies us with Christ’s death. This is why Paul so adamantly opposed the Judaizers who wished to impose circumcision upon Christians. Baptism is the sign of our having been circumcised in Christ. For this reason physical circumcision in the new covenant is unnecessary. Baptism identifies us with Christ's death and faith is the means by which we united to Christ.
Looking back on the first New Testament administration of the sacrament of baptism, we see Peter actually equate circumcision with baptism. How, you ask. Precisely because when Peter says, “the promise is to you and to your children, and all who are far off," he is using the exact same formula that God Himself used when He instituted the sacrament of circumcision in Genesis 17:7. And the Jews understood this clearly.