Galatians 5:9

A little leaven ... - This is evidently a proverbial expression; see it explained in the notes at I Corinthians 5:6. Its meaning here is, that the embracing of the errors which they had adopted was to be traced to some influence existing among themselves, and acting like leaven. It may either mean that there was existing among them from the first a slight tendency to conform to rites and customs, and that this had now like leaven pervaded the mass; or it may mean that the false teachers there might be compared to leaven, whose doctrines, though they were few in number, had pervaded the mass of Christians; or it may mean, as many have supposed, that any conformity to the Jewish law was like leaven. If they practiced circumcision, it would not stop there. The tendency to conform to Jewish rites would spread from that until it would infect all the doctrines of religion, and they would fall into the observance of all the rites of the Jewish law. It seems to me that the second interpretation referred to above is the correct one; and that the apostle means to say, that the influence which had brought this change about was at first small and unimportant; that there might have been but a few teachers of that kind, and it might have not been deemed worthy of particular attention or alarm; but that the doctrines thus infused into the churches, had spread like leaven, until the whole mass had become affected.