Russell Moore does a great job defending closed communion as a valid expression of “mere Christianity.” Here’s a little bit of it:
It seems sectarian to say one can’t come to the table unless one has been baptized by immersion as a believer, unless one realizes that, for Baptist Christians, this is what baptism is. Along with Eastern Orthodox Christians, Baptists affirm that Jesus meant “to immerse” when he commanded us to baptize. Unlike the Orthodox, Catholics, and the magisterial Reformers, Baptists believe a baptism is only valid when conferred on one who is in Christ, and who professes him as Lord. Ironically, it is here, where Baptists stand the most alone, that we are the most catholic.
Virtually every Christian communion in all places and at all times, Protestant, Catholic, or Orthodox, holds that baptism is a prerequisite to participation at the Lord’s Table. Regardless of our differences about the sacerdotal efficacy of baptism, we all acknowledge that this, at least, marks out the boundaries of church fellowship. There is, the apostle says, “one Lord, one faith, one baptism” (Eph. 4:5). In this, the dividing line isn’t whether one must be baptized to take the Supper, or whether one must be part of the church, but rather, what is “baptism” and what is “the church.”
At my church, we take communion every week, and we fence the table along these lines. We do it not because we like division, but because we think it’s good to obey the Lord’s command (Luke 22:19; cf. 1 Corinthians 11:27-29). Sometimes this leads to honest differences among Christians, but what is the alternative? Transgressing the Lord’s command by inviting unbaptized persons to take communion?
Baptists get the most heat for staying consistent with their ecclesiological convictions. After all, a paedobaptist Presbyterian could invite a Baptist to his communion table with no inconsistency, but a Baptist cannot do the same. This exclusion offends many brothers and sisters from different traditions, and so credo-baptism has become the step-child of the broader Christian community. The result historically has typically been the marginalization of Baptists. Spurgeon said it this way:
If I thought it wrong to be a Baptist, I should give it up, and become what I believed to be right. If we could find infant baptism in the word of God, we should adopt it. It would help us out of a great difficulty, for it would take away from us that reproach which is attached to us, that we are odd, and do not as other people do. But we have looked well through the Bible, and cannot find it, and do not believe that it is there; nor do we believe that others can find infant baptism in the Scriptures, unless they themselves first put it there.
-Charles Haddon Spurgeon, Susannah Spurgeon, Joseph Harrald,
The Autobiography of Charles H. Spurgeon, vol. 1
(Chicago: F.H. Revell, 1898), p. 155.
Read the rest of Moore’s article here.