Paul did not, as Peter had done, attempt to do something that he knew was completely contrary to the grace of God in an attempt to frustrate it. This verse is a powerful way of saying that the grace of God and the law are mutually exclusive and cannot be mixed together to provide a combined formula for salvation.
In helping to recover our brother who is going astray, we must use the strongest arguments available to us, arguments which are irrefutable and which will silence the gainsayer. However, we must at the same time do nothing to provoke a stubborn response by using unnecessary harshness. Paul speaks as gently as he can in that he applies these things to himself in the hope that Peter will learn from them. We are not told what the results of this rebuke was, but we can be sure that Paul’s courage was rewarded and that Peter acknowledged his error and repented of it, leading the way for all who had followed his bad example.
Did Paul overreact to Peter’s behaviour, and did he read too much into it? No, rather he saw more clearly than anyone else the implications of this very serious error, and he had the courage to speak and used just those words which were necessary to correct and recover one who was in danger of corrupting the gospel at a crucial point in the history of the evangelisation of the world. God at times seems to place the defence of his truth in the hands of a single man who must have the courage and conviction to stand against the whole world if necessary.