15:1 But some men came down from Judea and were teaching the brothers, “Unless you are circumcised according to the custom of Moses, you cannot be saved.” 2 And after Paul and Barnabas had no small dissension and debate with them, Paul and Barnabas and some of the others were appointed to go up to Jerusalem to the apostles and the elders about this question. 3 So, being sent on their way by the church, they passed through both Phoenicia and Samaria, describing in detail the conversion of the Gentiles, and brought great joy to all the brothers.  4 When they came to Jerusalem, they were welcomed by the church and the apostles and the elders, and they declared all that God had done with them. 5 But some believers who belonged to the party of the Pharisees rose up and said, “It is necessary to circumcise them and to order them to keep the law of Moses.” (Acts 15:1-5 (ESV)
This controversy just doesn’t solve itself overnight. Peter deals with it a couple times. And Paul does too.
It’s got to be hard for the Jewish people. There whole culture is being assaulted in the name of their Messiah. Can this be right? Christ was circumcised, but his followers don’t need to be? Christ ate kosher but his disciples don’t have to? The idea that Christ fulfilled the law on our behalf was a hard one to swallow. The Jews took as much pride in these laws as anyone does in their creed, in their code. Sure, there were times when the law became oppressive to the people. But for the most part they were proud of it, it separated them from others, it distinguished them. And God had given this law to them for their salvation.
For the Pharisees who had become Christian, there is something acute about the clash of the law with the gospel. But it is something that can be noticed even today. There is a tendency to use the gospel somewhat as a shield against one’s own particular sins, but then to think it doesn’t cover those other sins. It doesn’t cover your sins either. It forgives you. It forgives you who take pride in your law and think that somehow despite all the sin in your life, your creed makes you better, your personal code distinguishes you from those around you, and earns you favor with God. It forgives you that sin.