Galatians 2:11 But when Peter was come to Antioch, I withstood him to the face, because he was to be blamed.
12 For before that certain came from James, he did eat with the Gentiles: but when they were come, he withdrew and separated himself, fearing them which were of the circumcision.
13 And the other Jews dissembled likewise with him; insomuch that Barnabas also was carried away with their dissimulation.
We see in theses verses that even with the people who help establish the church, and preach Jews an gentile alike , even have disagreements. Paul was upset with Peter because he was turning his back on the gentile believers whom he had even eaten with because some of the legalistic Jews were not agreeing with what was being done. They were upset because they could not believe you could only be saved by grace and putting your faith in God. They felt that you could not totally abandon the law. These were Jews who had converted to Christianity and it was a little hard for them to totally forget the law. What really surprised Paul was that even Barnabas was siding with the legalistic Jews. All of this was happening in the early days of the church and you say struggles were expected. Even today form this we can relate this to a new convert who has lived in the world today for years, how easy it would be for them to slip back into some the bad habits they might have had if they do have someone to help them stay on the right path. This is why we need to be well grounded in the word of God.