... The justification of infant baptism in the Reformed churches hangs on the fact that baptism is the New Testament counterpart of circumcision.It was even more helpful to read his last paragraph in this chapter, which really reflects where I had ended up of my own accord, anyway!
There is in fact an important continuity between the signs of circumcision and baptism, but the Presbyterian representatives of Reformed theology seem to have undervalued the discontinuity. This is the root difference between Baptists and Presbyterians on baptism. I am a Baptist because I believe that on this score we honor botht the continuity and discontinuity between Israel and the church and between their respective covenant signs.
The continuity is expressed like this: Just as circumcision was administered to all the physical sons of Abraham who made up the physical Israel, so baptism should be administered to all the spiritual sons of Abraham who make up the spiritual Israel, the church. Consider the difference between the "old covenant" people of God and the "new covenant" people of God as Jeremiah and the author of Hebrews describe them. Both these Biblical writers say that under the new covenant one will not have to look at other members of the covenant and say, "Know the Lord," for to be a covenant member is to know the Lord. This implies that entry into the old covenant people of God was by physical birth, and entry into the new covenant people of God is by spiritual birth. It would seem to follow, then, that the sign of the covenant would reflect this change and would be administered to those who give evidence of spiritual birth...
Calvin and some of his heirs have treated signs of the covenant as if no significant changes happened with the coming of Christ. But God is forming His people today differently from when he strove with an ethnic people called Israel. The visible people of God are no longer formed through natural birth but through new birth and in expression through faith in Christ.
With the coming of John the Baptist and Jesus and the apostles, the emphasis now is that the spiritual status of our parents does not determine our membership in the covenant community. The beneficiaries of the blessings of Abraham are those who have the faith of Abraham. These are the ones who belong to the covenant community.
(Brothers, we are not Professionals, John Piper, pp.133-135)
Why have I dwelt on this? Because my sense is that many pastors, in order not to be contentious on this issue, neglect it almost entirely and do not call people to "repent and be baptized." What I am doing here is trying to model a responsible and reasonable defense of one view of baptism in the context of amicable and respectful relationships with those who hold other views. I think we need to teach our people the meaning of baptism and obey the Lord's command to baptize converts (Matt. 28:19), without elevating the doctrine to a primary one that would unduly cut us off from shared worship and ministry with others who share more important things with us.The whole article can be found on the Desiring God website.