What then does all of this have to do with baptism?
Everything. Under the old covenant, one could make a distinction between the physical and spiritual seed of Abraham (the locus of the covenant community is different from the locus of the elect). Under the old covenant, both “seeds” (physical and spiritual) received the covenant sign of circumcision and both were viewed as full covenant members in the national sense, even though it was only the remnant who were the true spiritual seed of Abraham. But this kind of distinction is not legitimate under the new covenant where the locus of the covenant community and the elect are the same. In other words, one cannot speak of a “remnant” in the new covenant community, like one could under the old covenant. All those who are “in Christ” are a regenerate people, and as such it is only they who may receive the sign of the covenant, namely baptism.
