After years of proclaiming the Gospel, Paul finally goes to Jerusalem to present his message to the original followers of Jesus, not because he has any doubts himself but because he feels compelled to do so by the Holy Spirit.
In the second half of Galatians 1 Paul asserts the God-givenness of his Gospel. The bare Gospel that Paul preaches is from God and therefore needs no further refinement or augmentation by humans. This is God’s good news first and foremost.
If we want to be plain spoken and unconcerned with pleasing men in the Pauline sense, what that means for us is that we should be bold in proclaiming the good news that Jesus has died for our sins and has been raised from the dead for our salvation.