The church in this passage is about 15 years old, since the ascension of Jesus Christ. Paul has been a Christian for about 6 years. The church has got a story to tell and they have good and bad days. They speak and people believe but the Jews were being legalistic and teaching the Greeks that circumcision was required to be saved.
We need to be a prayerful, watchful church and pray against attack from ideas that detract from the gospel. It starts with God. We cannot add anything to grace – it is all by grace, without it we have nothing. We have received the generous gift of forgiveness, we must continue to walk in it.