Dr. Mohler prefaces his criticism by reiterating the love and respect he has for Dr. Piper, and notes that they are able to "disagree without rancor or insecurity." He also commends the elders at Bethlehem for the openness with which they have sought feedback on their proposal. But goes on to explain why they are in profound disagreement over this issue:
That said, baptism has been understood by all major branches of Christianity, throughout the centuries of Christian experience, to be a requirement for church membership and the fellowship of the Lord’s table. Thus, for Baptists to receive into the membership of a Baptist church (or to invite to the Lord’s Supper) any believer who lacks such baptism, is to receive non-baptized persons as if they were baptized.
Any compromise of Baptist conviction concerning the requirement of believer’s baptism by immersion amounts to a redefinition of Baptist identity. More importantly, it raises the most basic questions of ecclesiology. We must give those questions intent attention in these days. Otherwise, will there be any Baptists in the next generation?
I personally believe that the clearness, prominence, and normativity of the Scriptural command for believer baptism in the church means that Dr. Mohler is correct on this.
It seems to me that the dilemmas for the Bethlehem elders--as those who believe that Scripture only teaches believer baptism--are these: Do they believe that baptism is a requirement for church membership (as virtually all churches through history have believed)? If the answer is no, then they are advocating a historically novel approach that has no precedence in Scripture. If the answer is yes, then the question becomes whether or not paedobaptism is a valid form of baptism. If the answer regarding the validity of paedobaptism is no, then only believer-baptized persons can become members. If the answer concerning the validity of paedobaptism is yes, then the very nature of baptism has been redefined and this without Scriptural warrant.
For me the issue comes down to the fact that while many considerations can be offered in favor of the proposal--considerations that surely give one pause--there does not exist (to my knowledge) any convincing case that the apostlolic writers themselves would countenance such a proposal. If such were to be proposed to them, I believe they would point to the clarity, prominence, and normativity of their command to be baptized as believers and for the church to be comprised of baptized believers. Now of course we can't go and just ask them. But they gave us instructios for building the church, and they did not send mixed signals on this front.
Those are my thoughts. I'd be curious for your take on the matter.