Peter knew that the Gentiles were no longer to be considered unclean (Acts 10:9-16), and he demonstrated this by eating with them. However, when some prominent Jews arrived, Peter “withdrew and separated himself, fearing them which were of the circumcision.” He knew better but allowed fear to cause him to rebel against the clear teachings of the Lord. As such, Peter “was to be blamed” (Galatians 2:11), and Paul had to rebuke him. It is one thing for a man to sin against the Lord through ignorance, but Peter knowingly, purposely, and openly violated God’s word. In like manner, believers today must bear the blame and the shame when they sin against the clear teachings of scripture.
A zealous person is contagious, both positively and negatively. The apostle Paul cautioned that the early believers had been zealously affected, but not in a good way. Those who opposed the gospel were adamant, yet they unwisely waged war against the truth. Night and day, they zealously fought in order to hinder the ministry of the believers. Ultimately, their zeal affected the people of God. These believers who started strong were hindered by the enemies' efforts to the point that it affected their race for the Lord (Galatians 5:7). Modern day enemies of the gospel are aware of this potential pitfall for the believers. They often display more zeal than those who knowingly possess the truth. Yet, today's passage also teaches that “it is good to be zealously affected always in a good thing.” Zeal breeds zeal. Zeal in righteousness will yield righteous results.