God Revealed it to Me

Galatians 2:2   I went there because God revealed to me that I should go....

Paul wants everyone to know that his trip to Jerusalem wasn't from his own planning or cunningness.  He was divinely instructed to go.  It was revealed to him by God to go.  This affirms Pauls mission wasn't from human initiation.  He is not working in conjunction with mens plans or even his own plans.  It also shows that his authority is a God given one.  It is the authority of divine revelation.  This reinforces Paul's point in 1:12 that the gospel Paul was given was through revelation.

Appointed by Christ not Men

 Gal 1:1  This letter is from Paul, an apostle. I was not appointed by any group of people or any human authority, but by Jesus Christ himself and by God the Father, who raised Jesus from the dead.

Paul is clearly stating where his authority to speak comes from.  He was appointed by Jesus.  He clarifies that his authority doesn't come from man.  So it doesn't come from prominent apostles like James and Peter.   His authority doesn't come through man.  In others words it isn't because some system called him a bishop or gave him an ordination.  Paul was appointed by the one who gives all true authority, Jesus Christ.

Paul sets out at the beginning to clarify his apostleship because it has been challenged by some.  Paul sets himself up to be on the same playing field as the twelve.

"the usual form of saluation is expanded by additions which answer to the occasion of the letter, and foreshadow its principal thoughts." 1

1 unknown commentary.