Read Titus 1 at Bible Gateway.
While Paul was instructing Titus on the qualities of true elders and false teachers, he says something interesting:
Therefore rebuke them sharply, that they may be sound in the faith, not giving heed to Jewish fables and commandments of men who turn from the truth. Tit 1:13-14
The “them” Titus is to rebuke, are the insubordinate, especially those of the circumcision (vs. 10). This is not the first time we have run across Paul’s struggle with the circumcision party:
While Peter was still speaking these words, the Holy Spirit fell upon all those who heard the word. And those of the circumcision who believed were astonished, as many as came with Peter, because the gift of the Holy Spirit had been poured out on the Gentiles also. Act 10:44-45
They were astonished, because God saved the Gentiles and baptized them with the Holy Spirit while they were still uncircumcised.
And when Peter came up to Jerusalem, those of the circumcision contended with him, saying, “You went in to uncircumcised men and ate with them!” Act 11:2-3
I looked for the command in Torah, the first five books of Moses, where God commanded His people not to eat with the uncircumcised, and couldn’t find it. There is, however, such a restriction in the Oral Law which the Jews brought back with them from Babylonia. The Torah contains the commandments of God, which Moses expressly charged the people not to add to or take away from them (Deu 4:2). The Oral Law contains the commandments of men.
Even Jesus was constantly at loggerheads with those who desired Him and His disciples to adhere to the Oral Law, which He also called the traditions of men (for example, as in this dispute over hand washing).
And certain men came down from Judea and taught the brethren, “Unless you are circumcised according to the custom of Moses, you cannot be saved.” Act 15:1
This is the circumcision party, who taught that conversion to Judaism and circumcision must precede salvation. Paul and Barnabas, the Scripture records here, had no small dissension with them.
Now when Peter had come to Antioch, I withstood him to his face, because he was to be blamed; for before certain men came from James, he would eat with the Gentiles; but when they came, he withdrew and separated himself, fearing those who were of the circumcision. Gal 2:11-12
Paul consistently taught in all the Gentile churches, that being circumcised does not save a man, and that right standing before God cannot be had by works of the flesh, but only by grace through faith in the finished work of Jesus Christ.
As many as desire to make a good showing in the flesh, these would compel you to be circumcised, only that they may not suffer persecution for the cross of Christ. For not even those who are circumcised keep the law, but they desire to have you circumcised that they may boast in your flesh. But God forbid that I should boast except in the cross of our Lord Jesus Christ, by whom the world has been crucified to me, and I to the world. For in Christ Jesus neither circumcision nor uncircumcision avails anything, but a new creation. Gal 6:12-15
Beware of dogs, beware of evil workers, beware of the mutilation! For we are the circumcision, who worship God in the Spirit, rejoice in Christ Jesus, and have no confidence in the flesh … Phi 3:2-3
In Him you were also circumcised with the circumcision made without hands, by putting off the body of the sins of the flesh, by the circumcision of Christ … Col 2:11
1 Corinthians 7:19
The circumcision made without hands, the circumcision of Christ, is the circumcision of the heart, toward which God through Moses and the Prophets continually exhorted the people (Lev 26:40-42, Deu 10:16, Deu 30:6, Psa 51:17, Isa 29:13-14, Jer 4:4, Jer 31:33, Eze 11:19-20).
And lest we should be confused that Paul is teaching that those who are saved ought to now disobey God as well as men:
Circumcision is nothing and uncircumcision is nothing, but keeping the commandments of God is what matters. 1 Cor 7:19
So we see that the false teachers taught a gospel of works for salvation, rather than a gospel of grace through faith. The false teachers taught adherence to the commandments of men as well as (or instead of) to the commandments of God. In Paul’s day, the ones who advocated works for salvation were Jews of the circumcision party. In our day the false teachers might be of a different sect, but the message of salvation by works and adherence the commandments of men rather than God has not changed.