The church in Corinth was young in the faith. It was also immature in many ways. We have seen that there were problems of divisions, factions and “party spirit”; now we see the problems of sexual immorality. A man was having a sexual relationship with his stepmother – a forbidden relationship. This is itself was bad enough, and Paul had stern words for that person. What was even worse, however, was the effect that this would have on the whole Christian community. Paul was horrified that the Church members were “self-satisfied” or boasting (v.6). How could a Christian community be self-satisfied when there was that kind of evil in their midst! It would seem that the effects of the evil had indeed begun to spread among them. Paul likens this effect to that of leaven (yeast): a very small amount of yeast affects the whole batch of dough. In the same way, the evil brought in by one person can affect the whole church. Just as when the children of Israel came out of Egypt they were commanded to get rid of all their old leaven, so that they could start a new life with new leaven, so now those who are to begin and to live a new life in Christ must get rid of the old leaven of sin and evil – completely.