Merely in the Flesh

Central to biblical theology is the distinction between the visible and invisible church. The Westminster Confession of Faith recognizes this doctrine in chapter 25, which summarizes Scripture’s differentiation between professing faith and possessing faith (Matt. 7:15–23; Rom. 9:6–13).

The visible church contains all who claim to be the Lord’s people, whether or not they have faith in God and His promises in Christ Jesus. The invisible church consists only of the elect who, by the Spirit, have trusted Jesus for salvation. Most times we cannot distinguish between those of faith and those who falsely claim to be in Christ. But God knows the wheat from the tares, and He will purify the visible church of non-believers at the resurrection (Matt. 13:24–30).

Today’s passage alludes to this distinction. Addressing covenant-breaking Judah, Jeremiah looks to a day when those circumcised in the flesh but not in the heart will be punished (Jer. 9:25–26). Circumcision of the body (outward) has always been useless without circumcision of the heart (inward). This sign and seal marking initiation into the covenant reveals the need for a heart cut away from sin and devoted to the Lord. As John Calvin comments, circumcision was “a sign both of repentance and faith.” Some, like Abraham, received the seal after trusting God. Others, like Isaac, were cut before confessing faith. But regardless of its timing, the sign brought no lasting benefits unless its recipient was inwardly converted.

The one covenant of grace unites believers of the old and new covenants (Rom. 3:30). Thus, many Reformed Christians apply the sign of new covenant initiation ­— baptism — to believing adults and their children. Knowing that covenant children are in closer proximity to Christ than a non-believer’s children (1 Cor. 7:14), and because the apostles never tell us to stop giving the covenant sign to children, infants are baptized to show they are set apart unto God. But like circumcision, this rite by itself only marks the child as a visible church member. Without faith the child never joins the invisible church, and judgment will befall him upon Jesus’ return (Matt. 7:21–23).