[This post is a continuation of the series, “How was Christ Administered in the Old Testament?”. The previous post may be accessed HERE.]
The covenant people in the Old Testament were mixed. They were all physical Israelites who were circumcised, but within that national-ethnic group there was a remnant of the true Israel, the true children of God (verse 8). This is the way God designed it to be: he bound himself by covenant to an ethnic people and their descendants; he gave them all the sign of the covenant, circumcision, but he worked within that ethnic group to call out a true people for himself.
The people of the covenant in the Old Testament were made up of Israel according to the flesh—an ethnic, national, religious people containing “children of the flesh” and “children of God.” Therefore it was fitting that circumcision was given to all the children of the flesh. (John Piper, “How do Circumcision and Baptism Correspond?”)
The above sentiment is arguably the largest barrier to Christians’ understanding circumcision as a means of administering the one redemptive work of Christ to the saints of the Old Testament. True, most all would agree that circumcision pointed to Christ in some sense, even marked out the seed line from which He would be born; but because they believe that the sign peculiarly marked out an ethnic, national, physical people, circumcision itself was not “sufficient and efficacious, through the operation of the Spirit, to instruct and build up the elect in faith in the promised Messiah, by whom they had full remission of sins, and eternal salvation” (Westminster Confession of Faith Ch. 7.5). If, as stated by Piper above, the Sign was a mere marker of “national-ethnic” physical descendants of Abraham, who only happened to contain a spiritual remnant called out by God, then clearly the Covenant Sign of Circumcision was not itself a means of administering the redemptive work of Christ. At best, the Sign merely narrowed the pool (and even that not exclusively).