“Also Circumcision and the Passover were, ever since their institution, means of grace for the period of the Old Testament. Regarding circumcision we read in Gen 17:7 :”I will establish My covenant between Me and thee and thy seed after thee in their generations for an everlasting covenant, to be a God unto thee, and to thy seed after thee.” That is to be your gracious God, assuring you of the remission of sins by this rite of circumcision. Therefore Paul, in Rom. 4:11, calls circumcision “a seal of the righteousness of the faith.”
And as concerns the Passover, Ex 12:21 ff. shows that the Children of Israel were exempted from the punitive judgment of God not because they were Jews, but because of the blood of the paschal lamb….
It is not true that the Sacraments of the New Testament differ from the Sacraments of the Old Testament as to their signification” [namely, as God-appointed signs of the grace of God]… “Both our and the fathers’ signs or Sacraments have a word of promise attached which calls for faith and can be fulfilled by no other work. Therefore they are signs or Sacraments of justification.”
(Pieper, Christian Dogmatics Vol. III pgs 214-15)
So often we take what Paul says about circumcision in the New Testament, and think this also applies to the believers in the time of the Old Testament. The problem Paul is addressing though in say galations is a problem that only comes up in the New Testament. He could not have made those same arguments even a few years earlier. Circumcision though had out lived its usefulness with the death and resurrection of Christ and the institution of Baptism. Yet people held on to it because of a false belief they had concerning it. Even though most of the men Paul has to rebuke had not recollection of the pain suffered at the hands of others in Circumcision, they made the faith, and circumcision into works that you have to do before you can be saved. Often times it is the same with baptism today. People make it into a work we do, and have to do. It is a work, but not ours, even when we are assenting to baptism it is the work of the Holy Spirit that brings us to the font.
In other words Circumcision and Baptism are very similar in this. In the Old Testament Circumcision and faith went hand in hand. Though it was possible to be circumcised and be an unbeliever, it was impossible to be a believer and still reject circumcision and the promises God attached to it. So it is with faith and Baptism in the New Testament. You cannot be a believer and at the same time denigrate baptism. It just doesn’t happen. God makes and attaches great promises of life and salvation to baptism. A believer will want to be baptized, and parents who believe will not stand in the way, but will harken to Peter’s words in Acts chapter 2 and not that the promises attached to baptism are for their children too. To denigrate baptism in such a way as to say it is not necessary is to mark yourself an unbeliever. To make it into a work of obedience etc. is to make the mistake of those whom Paul wished would mutilated themselves with their circumcision. The proper understanding is to see that baptism is God’s work with which he seals the promises of salvation to you.