1Paul, an apostle—not from men, nor through man, but through Jesus Christ, and God the Father, who raised him from the dead— 2and all the brothers who are with me, to the assemblies of Galatia: 3Grace to you and peace from God the Father and our Lord Jesus Christ, 4who gave himself for our sins, that he might deliver us out of this present evil age, according to the will of our God and Father— 5to whom be the glory forever and ever. Amen.
6I marvel that you are so quickly deserting him who called you in the grace of Christ to a different “good news”, 7but there isn’t another “good news.” Only there are some who trouble you and want to pervert the Good News of Christ. 8But even though we, or an angel from heaven, should preach to you any “good news” other than that which we preached to you, let him be cursed. 9As we have said before, so I now say again: if any man preaches to you any “good news” other than that which you received, let him be cursed.
10For am I now seeking the favor of men, or of God? Or am I striving to please men? For if I were still pleasing men, I wouldn’t be a servant of Christ.
11But I make known to you, brothers, concerning the Good News which was preached by me, that it is not according to man. 12For I didn’t receive it from man, nor was I taught it, but it came to me through revelation of Jesus Christ. 13For you have heard of my way of living in time past in the Jews’ religion, how that beyond measure I persecuted the assembly of God and ravaged it. 14I advanced in the Jews’ religion beyond many of my own age among my countrymen, being more exceedingly zealous for the traditions of my fathers. 15But when it was the good pleasure of God, who separated me from my mother’s womb and called me through his grace, 16to reveal his Son in me, that I might preach him among the Gentiles, I didn’t immediately confer with flesh and blood, 17nor did I go up to Jerusalem to those who were apostles before me, but I went away into Arabia. Then I returned to Damascus.
18Then after three years I went up to Jerusalem to visit Peter, and stayed with him fifteen days. 19But of the other apostles I saw no one except James, the Lord’s brother. 20Now about the things which I write to you, behold, before God, I’m not lying. 21Then I came to the regions of Syria and Cilicia. 22I was still unknown by face to the assemblies of Judea which were in Christ, 23but they only heard, “He who once persecuted us now preaches the faith that he once tried to destroy.” 24So they glorified God in me.
The word "apostle" (apostolos, αποστολος) is from the Greek word apostello (αποστελλω), meaning to send. Paul saw himself from the time of his commission by Jesus, and confirmation in Damascus, as one who was sent by God and not by his personal desire and was equal to being one of "the twelve" that Jesus originally commissioned (other than Matthias, Acts 1:26).
To be designated as an apostle, the apostle Peter stated the standards required in Acts 1:21-25. He said in verses 21-21 that one to be an apostle required that the man must have been with the apostles from the beginning of Jesus' ministry, beginning at the baptism of John through the resurrection and ascension of Jesus to heaven. An essential addition requirement for an apostle is stated in verses 23-25, the person would be chosen with God's approval.
Paul was of a unique apostle (1 Cor 15:7-10), as the apostle to the Gentiles, and he said that one who was an apostle did the works of an apostle in 2 Cor 12:11-12.