People make the same mistake whenever they detach the sign from the thing signified. So they do with baptism when they treat it as a sacrament, something that possesses efficacy in itself, as if it could bring about a real spiritual cleansing, even though unaccompanied by faith in Christ. So they do with the mass when the elements are treated as if they could give life by a superstitious physical act of eating and drinking. So they do with the altar call, when the response to the gospel is only an outward movement without any repentance in the heart, and yet the person is assured that they are saved. And so they do in the Catholic rite of confession to a human priest, and there is no real contrition in the heart towards God.
What does Paul mean when he says, ‘if thou keep the law’? This is interpreted in two different ways. Some treat this as a hypothetical statement, something that could never happen in reality, a perfect keeping of the law, which would give man a legal righteousness if it were possible, which it is not. In that case circumcision would be profitable, because, without contributing to righteousness itself, it would be the sign of a righteousness that obtains life by works. It is true that Paul sees circumcision this way when he says, ‘I testify again to every man that is circumcised, that he is a debtor to do the whole law’ (Galatians 5:3), but in Galatians the subject is justification. That subject will come later in the Epistle to the Romans, but the context here is different. Here Paul is in the middle of a passage in which he is proving that God is no respecter of persons; that it is not enough to hear the law, but that a man must also do it. The argument here is not hypothetical. He has spoken of Gentiles which do not have the law, doing by nature the things contained in the law. He will go on in the remainder of this chapter to speak of the uncircumcision who keep the righteousness of the law. He is speaking of those who have committed in their hearts before God to obey his law, to make Christ their Lord. He is not talking about a perfect obedience, or a legal righteousness obtained from the law. These are people who have been justified by faith, and are now living to please God. For them circumcision is profitable, because it has led to their also being circumcised in their hearts, and they stand justified by grace in the sight of God.
Why was circumcision made the sign of two such different covenants? It was a sign of the Abrahamic covenant (Genesis 17:10, 12; 21:4), and it was also a sign of the Mosaic covenant made with Israel (Leviticus 12:3; Galatians 5:3), and every stranger that joined themselves to Israel was also to be circumcised (Genesis 17:27; Exodus 12:48). But the Abrahamic covenant was an administration of the covenant of grace (Galatians 3:7), and the Mosaic covenant was a legal covenant, an administration of the covenant of works (Galatians 3:10). These two covenants were of entirely different natures and opposed to one another (Romans 11:6; Galatians 3:18). So how could circumcision be the sign of both of them – for there is no doubt that that was the case, and Christ confirms it (John 7:22)? Why then was circumcision which was originally an evangelical sign, taken and used again for such a different covenant? To answer this we must understand that there were two parts to the Abrahamic covenant. There was an evangelical part in which spiritual promises were made and real blessings conferred and true saving faith required. But there were also earthly promises made to an earthly people, who were not regenerate and who were not the spiritual seed of Abraham, but were no more than his earthly children, his physical descendants. These were promised earthly blessings, which were a type and pledge of God’s willingness to give the heavenly equivalent to those who exercised faith. For those who were Abraham’s physical descendants but who did not yet have faith, the national covenant made with Israel was like a school, and the purpose of that school was to bring them to faith. The school started with the Abrahamic covenant, but it reached its most developed form in the Mosaic covenant. It was a school equipped with all manner of visual aids, all of which pointed to evangelical faith. Once an individual came to evangelical faith they would, in a sense, graduate out of the school. The visual aids were all the symbolism of the ceremonial law. Nevertheless, while students were in the school they remained under the law, and it was perfectly possible that some would never graduate. This was in fact the outcome for the vast majority of the Jews who treated the ceremonial law and circumcision as an end in itself. But along with the ceremonial law went the moral law with all its demands of perfect obedience which they could never keep. Circumcision in the flesh was intended to lead people to circumcision of the heart (Deuteronomy 10:16; 30:6; Jeremiah 4:4), but if it failed to do so, then the individual remained under the law, and under the condemnation of the law. It was entirely right therefore that those descendants of Abraham who did not walk in the footsteps of Abraham’s faith were reminded that they were still under the law, and it was entirely appropriate that circumcision in the flesh was made a sign of the national covenant, and of the obligation to continue to do all things written in the book of the law (Galatians 3:10), for if a person will not trust in Christ for salvation, he remains under the law. The Jew must not think that his descent from Abraham gave him any real benefit without faith.