Chuck Swindoll in his commentary writes:
“The Apostle Paul does not do this to simply hang out the church’s dirty laundry or to meet some ideal of “total transparency”. Paul knows like anybody else that not everything should be broadcast to the public. Furthermore, Paul certainly isn’t trying to hang Peter out to dry..…..
So, what motivated Paul to report his conflict with Peter to the troubled churches in Galatia?
The key to answering the first question comes from one small word: BUT.”
Chuck Swindoll refers to verse 12
“For BEFORE certain men came from James, he was eating with the Gentiles, BUT when they came, he drew back and separated himself, FEARING the circumcision party.
We could call it Peer-pressure from his Jewish friends. Fear of rejection by his Jewish friends. You see, in Jerusalem, under James, “which was known as “JAMES THE JUST” because of the unimpeachable devotion he exhibited among the Jewish people.” (John Stott, “The message of Galatians”)
John Stott provides some insight into the assumptions of this question found in Galatians 2:17
“Paul’s critics argued like this: “Your doctrine of justification through faith in Christ only, apart from the works of the law, is a highly dangerous doctrine. It fatally weakens a man’s sense of moral responsibility. If he can be accepted through TRUSTING IN CHRIST, without any necessity to do good works, you are actually encouraging him to break the law, which is the vile heresy of antinomianism”. People still argue like this today: “If God justifies bad people, what is the point of being good? Can’t we do as we like and live as we please?”
As Chuck Swindoll wrote in his commentary:
“But what seems like a sturdy staircase built to lead us to God’s favor actually turns out to be a rotten wooden trap that will crumble beneath us. As Paul explains, only the cross of Christ can give us the assurance we need to step out in faith and live a truly grace-filled life.
Our justification, sanctification, and future glorification are all results of God’s grace alone, effected through faith alone, in the finished work of Christ alone.