GALATIANS: Paul's Apostolic Authority Established; "God, who separated me from my mother’s womb and called me through His grace, to reveal His Son in me, that I might preach Him among the Gentiles!"

Then he came to Derbe and Lystra. ...they had gone through Phrygia and the region of Galatia,... (Acts 16:1, 6) And when he had landed at Caesarea, and gone up and greeted the church, he went down to Antioch. After he had spent some time there, he departed and went over the region of Galatia and Phrygia in order, strengthening all the disciples. (Acts 18:22-23)

Paul had started the church in the region of Galatia, but he had not been able to spend as much time there as he had in other areas where he had started churches. While he was with them, his message was clear that salvation came solely through faith in Christ Jesus. There is nothing else we can do or add to salvation!  However, certain Jewish religious leaders from Palestine, Judaizers had come after Paul left and tried to convince the church that there were additional things they needed to do in order to be saved. Of course, Paul was going to clarify everything in no uncertain terms.

Paul, an apostle (not from men nor through man, but through Jesus Christ and God the Father who raised Him from the dead), and all the brethren who are with me,
To the churches of Galatia: Grace to you and peace from God the Father and our Lord Jesus Christ, who gave Himself for our sins, that He might deliver us from this present evil age, according to the will of our God and Father, to whom be glory forever and ever. Amen. (Galatians 1:1-5)

I marvel that you are turning away so soon from Him who called you in the grace of Christ, to a different gospel, which is not another; but there are some who trouble you and want to pervert the gospel of Christ. (Galatians 1:6-7) After the pleasantries, Paul got straight to the point. But even if we, or an angel from heaven, preach any other gospel to you than what we have preached to you, let him be accursed. As we have said before, so now I say again, if anyone preaches any other gospel to you than what you have received, let him be accursed. (Galatians 1:8-9)

For do I now persuade men, or God? Or do I seek to please men? For if I still pleased men, I would not be a bondservant of Christ. But I make known to you, brethren, that the gospel which was preached by me is not according to man. For I neither received it from man, nor was I taught it, but it came through the revelation of Jesus Christ. (Galatians 1:10-12)  One of the things the Judaizers had told the Christians in the region of Galatia was that Paul was not a true apostle because he was not one of the original twelve.

Remember the requirements of being an apostle, as explained by Peter when the disciples chose a replacement for Judas Iscariot, "of these men who have accompanied us all the time that the Lord Jesus went in and out among us, beginning from the baptism of John to that day when He was taken up from us, one of these must become a witness with us of His resurrection.” (Acts 1:21-22) Well, Paul hadn't accompanied the disciples all the time that the Lord Jesus went in and out among them, but he had witnessed His resurrection. As he journeyed he came near Damascus, and suddenly a light shone around him from heaven. Then he fell to the ground, and heard a voice saying to him, “Saul, Saul, why are you persecuting Me?” And he said, “Who are You, Lord?” Then the Lord said, “I am Jesus, whom you are persecuting. It is hard for you to kick against the goads.” (Acts 9:3-5)

So he, trembling and astonished, said, “Lord, what do You want me to do?” Then the Lord said to him, “Arise and go into the city, and you will be told what you must do.” Now there was a certain disciple at Damascus named Ananias; and to him the Lord said in a vision, “Ananias.” And he said, “Here I am, Lord.” So the Lord said to him, “Arise and go to the street called Straight, and inquire at the house of Judas for one called Saul of Tarsus, for behold, he is praying. And in a vision he has seen a man named Ananias coming in and putting his hand on him, so that he might receive his sight.” ... “Go, for he is a chosen vessel of Mine to bear My name before Gentiles, kings, and the children of Israel. For I will show him how many things he must suffer for My name’s sake.” (Acts 9:6, 10-12, 15-16)

Paul was appointed an apostle directly by Jesus Christ, and he went on to reiterate that fact. For you have heard of my former conduct in Judaism, how I persecuted the church of God beyond measure and tried to destroy it. And I advanced in Judaism beyond many of my contemporaries in my own nation, being more exceedingly zealous for the traditions of my fathers. But when it pleased God, who separated me from my mother’s womb and called me through His grace, to reveal His Son in me, that I might preach Him among the Gentiles, I did not immediately confer with flesh and blood, nor did I go up to Jerusalem to those who were apostles before me; but I went to Arabia, and returned again to Damascus. [Acts 9:1-25] (Galatians 1:13-17)

Then after three years I went up to Jerusalem to see Peter, and remained with him fifteen days. But I saw none of the other apostles except James, the Lord’s brother. (Now concerning the things which I write to you, indeed, before God, I do not lie.) Afterward I went into the regions of Syria and Cilicia. And I was unknown by face to the churches of Judea which were in Christ. But they were hearing only, “He who formerly persecuted us now preaches the faith which he once tried to destroy.” And they glorified God in me. [Acts 9:26-31] (Galatians 1:18-24)

Now that Paul had "established his apostolic authority", he would go on to explain how we are saved through faith in "Christ's atoning work rather than by the works of the law", as the Judaizers had convinced the church in the region of Galatia...