Here Paul defends his message. He has already stated that there is only one gospel, but he is now forced to answer, "Why should yours be the only one?"
Since there is only one gospel, why could not an entirely different gospel be the right one? Paul's defense is to stress the origin of his message, and verse 10 is a transition that leads into his answer. What he preached was not done to please men at the expense of the message.
We must understand that when Paul traveled into an area, he did not just blast his audiences with everything that he knew. I Corinthians 9:19-23 informs us that he did all that he could to please people, to cultivate their appreciation of him, but even though he did these things, he never equivocated with what is true.
Acts 17 contains a good example of this. Paul began by speaking to the Athenians about their gods, even admitting to them that they were very religious. He noted all the statues around the Areopagus and highlighted that one was inscribed TO THE UNKNOWN GOD. "I see you have a statue here TO THE UNKNOWN GOD. Well, I am here to tell you about that unknown God."
Paul never equivocated about the message, but he did approach people in such as way as to catch their ear and begin to get them to assent to what he was saying. He is not saying that he was always successful in doing this, only that he never equivocated about the message. He never preached merely to appeal to people, but the message he gave was always the truth of God.
John W. Ritenbaugh
The Covenants, Grace, and Law (Part 24)
Other Forerunner Commentary entries containing Galatians 1:10: