No outward sign, like that of circumcision, can fix you if your heart is not close to God. In the Old Testament, circumcision was intended to be a sign of the covenant with God, but even then, God made it clear His focus was on the heart. Christ has already accomplished this act of circumcision in the inner man of the Christian, freeing us and conforming us to His covenant perfectly, as only He can. Why would we need to add to what He has done in us? Christ set us free.