This was probably Paul’s first pastoral letter to a group of churches in what is now eastern Turkey.  In particular, the churches which Paul had helped plant in south Galatia: Psidian Antioch, Iconium, Lystra and Derbe  (Acts 13:13-14; Acts 14:19-25) and where he suffered persecution.  These towns were not too far from Tarsus, Paul’s home-town to which he returned after meeting Jesus on the road to Damascus (Acts 9:30).

Paul did not claim his own authority, or the appointment from any council, but he had accepted a personal commission from Father God and Jesus Christ (Acts 26:16-20) – a commission to bring the gospel to the Gentiles (Acts 22:21).  However, some people refused to accept Paul’s preaching and writing as being truth from God.  People who did not like what God said through him would ridicule him and despise his message.  So, Paul described the source of his apostolic authority – it came directly from Jesus Christ, the Son of God and God the Father.
 
Paul wanted to make clear that the Jesus he preached had been physically raised from the dead by God’s mighty power.  His resurrection message was not a human philosophy derived from other people, or a personal life which he had invented.  What he preached and wrote was true, backed by eye-witness accounts, and was directly inspired by God.  Paul had been personally commanded to deliver his messages by Christ, who confronted him on the road to Damascus (Galatians 1:11-20).
 
The apostles were all appointed by Jesus and had met Him after His resurrection.  They were witnesses to the power of God in raising the dead.  Paul’s encounter was dramatic, and his apostolic training was unique and personal.  Yet when he met with Peter ('Cephas' in Greek) and James three years later (Galatians 1:18-19), his understanding of the gospel was identical to theirs!  In part, it was God’s way of validating Paul’s ministry.  God is still speaking through Paul’s writings because He inspired His apostle.  So Paul’s words are God’s words to us, and we cannot ignore them without distorting the Word of God.