You were running well. Who hindered you from obeying the truth? This persuasion is not from him who calls you. A little leaven leavens the whole lump. I have confidence in the Lord that you will take no other view, and the one who is troubling you will bear the penalty, whoever he is. But if I, brothers, still preach circumcision, why am I still being persecuted? In that case the offense of the cross has been removed. I wish those who unsettle you would emasculate themselves!
The Galatians started out on the right track. They were doing well in believing and following the Gospel of Christ. They were living in the freedom that Christ's sacrifice provides. But then things took a wrong turn. Not that they were hindered. Who (or what) hindered them? Was it the same voice that whispered to Eve in the garden? Or was it more like the voice that spoke to Adam? (I am not referring to the fact that Eve was a woman here, but rather that she was a victim of the lies of Satan, and as such was a human voice to a lie.)
A little leaven leavens the whole lump. Regardless of where the voice started, it works its way through the entire batch of dough, infecting the good dough. That is what happened in Galatia, they were following the gospel that Paul had laid before them, when some whispering voices came in, appealing to their "reason," and said things that lead them from grace to legalism. Voices that whispered, "God doesn't love you enough, you have to try harder," or "grace alone will not suffice, how does that make sense," and other such nonsense.
Paul was convinced that with a little guidance, they would return to the truth of the gospel message. He even asks why he was being persecuted if he still preached circumcision? If Paul preached circumcision, or any other type of legalism, the Jews would not be persecuting him, because his preaching would not offend them. No bloody cross of Christ, no offense!
I will leave you to your own thoughts about verse 12. All I can say is that I like Paul, a real straight shooter with an awesome sense of humor.