Galatians 1:11-17

v11-12: Our knowledge of the gospel comes from God's Word and we grow in our understanding of it through the teaching and instruction of those who preach it to us.  It was different for the Paul. "He received both his knowledge of the Gospel and his authority to preach it directly from the Lord Jesus himself." It came to him by direct "revelation from Christ."  Paul makes this point as proof that he is an apostle.

v13-17: It is not enough to have Christ revealed to us, we need Christ revealed in us.  It is the power and grace of God that can turn a sinner from the error of their ways and effectually call them to faith in Christ.  Those whom God calls to faith in Christ, He has a purpose for, which in Paul's case, was to preach the gospel to the Gentiles.