In the agreement of Galatians 2:9 that Paul and Barnabas should go to the heathen while James, Cephas and John would go to the circumcision, it is important to understand who Paul considered to be heathen and who were the circumcision. If the Galatians 2 agreement is the recounting of the Acts 15 council, then notice right after this agreement Paul sets out on his second apostolic journey and Acts 17:1,2 says: “Now when they had passed through Amphipolis and Apollonia, they came to Thessalonica, where was a synagogue of the Jews: And Paul, as his manner was, went in unto them, and three sabbath days reasoned with them out of the scriptures.” Apparently, Paul considered lost Jews as heathen and “the Circumcision” as the believing remnant prior to him.
In Galatians 1 Paul gives a detailed account of his gospel, as to how he received it and his limited contact with the other Apostles before him. The three years in Damascus/Arabia/ back to Damascus is certainly when he received his gospel. As early as Galatians 1:21 he had made known that gospel in Syria and Cilicia. That is why the council in Acts 15 addressed their letter to “the brethren which are of the Gentiles in Antioch and Syria and Cilicia.” Paul’s first recorded preaching in Acts 13 is after the time spent in Antioch, Syria and Cilicia. There is where we find his gospel message: “Be it known unto you therefore, men and brethren, that through this man is preached unto you the forgiveness of sins: And by him all that believe are justified from all things, from which ye could not be justified by the law of Moses” (Acts 13:38,39); but he had certainly preached that message already in those other places. So Acts 9 is where Paul’s gospel of the grace of God began to be preached.
We know that Peter’s gospel of the Kingdom was preached during Christ’s earthly ministry (Matthew 4:17,23; 10:2-7). Note it will be preached again during the future tribulation (or 70th week of Daniel) as seen in Matthew 24:14. The Twelve Apostles began to preach this good news in Acts 1-7, but in Acts 7:54-60 when the Lord Jesus stood and the “day of the Lord’s wrath” did not begin, that Kingdom was postponed. The good news that it was “at hand” could no longer be proclaimed. However, these promises to the believing remnant (the circumcision) continued to be affirmed by James, Peter and John as they agree and as they wrote in their epistles to them –
“Wherefore I will not be negligent to put you always in remembrance of these things, though ye know them, and be established in the present truth. Yea, I think it meet, as long as I am in this tabernacle, to stir you up by putting you in remembrance; Knowing that shortly I must put off this my tabernacle, even as our Lord Jesus Christ hath showed me. Moreover I will endeavour that ye may be able after my decease to have these things always in remembrance. For we have not followed cunningly devised fables, when we made known unto you the power and coming of our Lord Jesus Christ, but were eyewitnesses of his majesty. For he received from God the Father honour and glory, when there came such a voice to him from the excellent glory, This is my beloved Son, in whom I am well pleased. And this voice which came from heaven we heard, when we were with him in the holy mount. We have also a more sure word of prophecy; whereunto ye do well that ye take heed, as unto a light that shineth in a dark place, until the day dawn, and the day star arise in your hearts:” (II Peter 1:12-19).