The Early Church had a controversy with a group called “the Judaizers” who were teaching justification by works of the law.
And certain men which came down from Judaea taught the brethren, and said, except ye be circumcised after themanner of Moses, ye cannot be saved. (Acts 15:1)
In other words, they taught that Gentiles need to obey the law (the Torah) and perform the works of the law (circumcision) in order to be justified. Since Paul’s ministry was to the Gentiles, he dedicated a large portion of his writings in Romans and Galatians, which were to Gentile Churches, to write against the Judaizers.
You will notice that Paul continually mentioned circumcision when discussing justification by works of the law in both Romans and Galatians.
Therefore we conclude that a man is justified by faith without the deeds of the law. Is he the God of the Jews only? (Those who had the Torah) Is he not also of the Gentiles? (Those who did not have the Torah) Yes, of the Gentiles also. Seeing it is one God, which shall justify the circumcision by faith, and the uncircumcision through faith. (Rom. 3:28-30)
Cometh this blessedness then upon the circumcision only or upon the uncircumcision also? For we say that faith was reckoned to Abraham for righteousness. How was it then reckoned? When he was in the circumcision, or in uncircumcision? Not in circumcision, but in uncircumcision. (Rom. 4:9-10)
Paul is arguing that Abraham was justified before circumcision, before the law of circumcision was given, and therefore the Gentiles too can be justified by faith without the work of the law of circumcision.
For in Christ Jesus neither circumcision availeth any thing, nor uncircumcision, but a new creature. (Gal. 6:15)
For in Jesus Christ neither circumcision availeth anything, nor uncircumcision; but faith which worketh by love. (Gal. 5:6)
Circumcision is nothing and uncircumcision is nothing, but the keeping of the commandments of God (1 Cor. 7:19).
Paul continually and repeated referred to circumcision when discussing justification “by works of the law” and said that circumcision does not “availeth anything” and is “nothing” but what matters is “a new creature” “faith which worketh by love” and “keeping of the commandments”.
It needs to be understood that Paul was not coming against the preaching of repentance in his epistles when he discussed justification by works of the law. In Galatia the Judaizers came and convinced the Gentile Church there that they needed to be circumcised in order to be saved. Paul wrote his epistle to the Galatians to correct this error of the Judaizers. It was not that the Galatians were repenting of their sins and Paul thought, “I better put a stop to this”. Paul certainly would not have any problem with Gentiles repenting of their sins since his God given ministry was to bring the Gentiles to repentance (Acts 26:20). When Paul preached to the Gentiles in Athens, he told them that God was calling all of them to repent (Acts 17:30). Paul said that we needed to be circumcised, not in our flesh, but in our hearts (Rom. 2:28-29). The circumcision of the heart is putting off your sins (Col. 2:11). Paul bemoaned those Gentiles in Corinth who had not repented of their uncleanness and fornication (2 Cor. 12:21). Paul explicitly said that we should not continue in our sins (Rom. 6:1-2) but that we should awake to righteousness and stop sinning (1 Cor. 15:34). Paul even warned the Galatians that if they lived sinful lives, they would not inherit the kingdom of God (Gal. 5:19-21). It was the Apostle Paul who said “after thy hardness and impenitent heart treasurest up unto thyself wrath” (Rom. 2:5), and that “repentance” leads “to salvation” (2 Cor. 7:10). Clearly Paul would not have had any problems with Gentiles repenting of their sins. Rather, Paul was upset that the Gentile Church in Galatia started to believe falsehoods from the Judaizers about how to be saved.
A good example of how Gentiles find the forgiveness of sins is the story of Nineveh. The narrative records that the people believed God (Jonah 3:5) and turned from their sins (Jonah 3:8). When God saw this, He changed His plans and decided not to destroy them as He said He would (Jonah 3:10). These Gentiles did not need to adopt the Jewish customs, obey the Torah, or be circumcised in order to be pardoned. They were saved, or found the mercy of God, through simple repentance from sin and faith in God. Jesus even said that sinners will be condemned if they do not repent the way Nineveh did (Matt. 12:41). Therefore the way that Gentiles were saved through repentance and faith in the Old Testament is the same way that they are saved in the New Testament, according to Jesus. Repenting of sin is required in both the Old and New Testament as Jesus said and therefore repentance is not the works of the law Paul preached against.
We know that Jesus Christ taught repentance (Lk. 13:3) and Paul certainly would not have contradicted Jesus Christ since Paul was an Apostle of Jesus Christ (Eph. 1:1; Col. 1:1). Paul explicitly said that men ought to listen to the wholesome words of Jesus (1 Tim. 6:3). Paul was by no means attacking the preaching of repentance when he wrote against justification by works of the law. Paul was attacking the Judaizers and their false gospel that Gentiles must convert to Judaism, be circumcised, and obey the Torah.
Thanks to Jesse Morell