“There is one body and one Spirit, just as also you were called in one hope of your calling; one Lord, one faith, one baptism” (Ephesians 4:4-5).
Federal Visionists love this verse because they think that Paul is saying that there is only one baptism, that is, that water baptism and spirit baptism are identical. Or, as one Light-hearted Federal Visionist often says, “baptism is baptism.” Obviously, this is a regurgitation of the Roman Catholic heresy of baptismal regeneration.
The Reformed faith has always held that there are two baptisms: water baptism and Spirit baptism. Spirit baptism is where the action is: regeneration, union with Christ, Covenant of Grace Membership, Invisible Church Membership, etc. Water baptism is where you get wet in front of the church.
Anyone should be able to see the clear difference between these two kinds of baptism. The failure to distinguish water baptism from spirit baptism means that you have exited the Reformed freeway and are now on the Roman road, ecclesially speaking.
One of the great things about the current Anti-Federal Visionist reign of terror is that it unites all Christians under the label “Reformed,” including Baptists (as long as you are willing to be called a “Reformed Baptist”). This is because baptism has nothing to do with being Reformed. Thus, a Reformed Baptist is just as Reformed as a Presbyterian. There’s no difference!
Sure, there are superficial differences in their practice of baptism: Reformed Baptists use a lot of water whereas Presbyterians only use a little. Presbyterians baptize babies whereas Reformed Baptists only baptize the elect.
While their practices differ, their doctrines of baptism are virtually identical, separated mostly by semantics. Presbyterians sometimes talk about baptism as a “means of grace,” but after thoroughly qualifying this, they are on the same ground as Reformed Baptists.
Thus, the key to being Reformed is whether you are a Tulipist or not. (Side note: we hesitate to say Calvinist because Calvin’s view of baptism may have been proto-FV. We’re not sure because we don’t bother reading primary sources anymore. Better to site Reformed scholars like Kuyper and Ryrie).
In summary, to be Reformed, you only have to believe in TULIP. That’s it! Everyone who is Tulipistic is Reformed. Here’s an easy tautology to remember this:
Reformed = TULIP
Getting back to the task at hand, what Paul means by “one baptism” is that there is one real baptism or one genuine baptism, which is, of course, Spirit baptism. While water baptism is probably important for some reason, Spirit baptism is the only one that really counts.
(See here for how to circumvent the obviously-Tridentine language of the Nicene Creed.)