Galatia was a central province of Asia minor and was visited by Paul on his first missionary journey (see 14.1 Acts-20), also in the second journey (acts 15.46-16.5) and again in the third voyage (18.23 Acts).
The major cities were Iconium, lystra, Derbe and probably Antioch of Pisidia generally believes that the Epistle was written after the third trip, more or less in the year 57 A.D., but not sure.
The churches in those cities were founded by Paul, but were being disturbed by Jewish teachers, who were trying to decrease the Apostolic authority of Paulo and insisted on that Christians keep the Mosaic law (circumcision, guard days, abstaining from certain foods etc.) to be saved. In the epistle, Paul establishes his apostolic authority and refute the false teachings of the Loyalists.
Paul begins the letter, stating their apostolic authority that came from God the father and son and not of men. His companions would be perhaps mentioned in acts 20.4. The greeting "grace and peace" in the Epistles (and always in the same order) refers to two gifts from the father and the son: and by divine favor (not by works of the law) we can have peace with God.
Jesus Christ willingly died for our sins, to drag us (separate all) of this world of disobedience to God. 0 Gospel calls us to upgrade, but for deliverance. So, God is glorified!
Instead of giving thanks to God for the spiritual progress of those believers (as he always did in Epistolas to other churches), Paul declares himself amazed by the speed with which the Galatians were being persuaded to follow a doctrine that was a perversion of the Gospel of Christ-the one true Gospel, which even an Angel from heaven has the right to change and much less men.
The Gospel announced by the Apostles is the free salvation by faith in Christ as Lord and Savior divine-cannot be increased or decreased. The divine curse ("anathema") would be the fate of Angel, Apostle or preacher who the change.
This solemn warning is in effect until the present day, in which Mormons, Adventists and various sects of mystical cult of transcendentalism and many decrees and teachings of Christianity in General "go beyond" the Gospel that Christ and the Apostles preached.
How far should the preaching of the Gospel "pleasing" to listeners? (v. 10). Eloquence, rhetoric, the personality of the preacher-these things can attract listeners; However, what I like most is the truth, sure of what biblical preaches. Otherwise, not preaching like the God, nor to the faithful believers.
It is not surprising that everyone "glorified God" for the conversion of such an implacable enemy (v. 24).
1 Paul, an apostle (not from men nor through man, but through Jesus Christ and God the Father who raised Him from the dead),
2 and all the brethren who are with me, To the churches of Galatia:
3 Grace to you and peace from God the Father and our Lord Jesus Christ,
4 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,
5 to whom be glory forever and ever. Amen.
6 I marvel that you are turning away so soon from Him who called you in the grace of Christ, to a different gospel,
7 which is not another; but there are some who trouble you and want to pervert the gospel of Christ.
8 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.
9 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.
10 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.
11 But I make known to you, brethren, that the gospel which was preached by me is not according to man.
12 For I neither received it from man, nor was I taught it, but it came through the revelation of Jesus Christ.
13 For you have heard of my former conduct in Judaism, how I persecuted the church of God beyond measure and tried to destroy it.
14 And I advanced in Judaism beyond many of my contemporaries in my own nation, being more exceedingly zealous for the traditions of my fathers.
15 But when it pleased God, who separated me from my mother's womb and called me through His grace,
16 to reveal His Son in me, that I might preach Him among the Gentiles, I did not immediately confer with flesh and blood,
17 nor did I go up to Jerusalem to those who were apostles before me; but I went to Arabia, and returned again to Damascus.
18 Then after three years I went up to Jerusalem to see Peter, and remained with him fifteen days.
19 But I saw none of the other apostles except James, the Lord's brother.
20 (Now concerning the things which I write to you, indeed, before God, I do not lie.)
21 Afterward I went into the regions of Syria and Cilicia.
22 And I was unknown by face to the churches of Judea which were in Christ.
23 But they were hearing only, "He who formerly persecuted us now preaches the faith which he once tried to destroy."
24 And they glorified God in me.
Galatians chapter 1 verses 1 to 24