Galatians 5:9

A little leaven leaveneth the whole lump. A little leaven communicates its bitterness to the whole mass of meal. This is a maxim describing the way that a vicious part spoils the whole, and of course is capable of general application. In 1Co 5:6 it is applied to the fornicator who was corrupting the whole Corinthian Church, and here it is applied to the Judaisers, who are being dealt with throughout this chapter, and declares that they are corrupting the whole of the Galatian Church. Jerome says: " Arius in Alexandria was but a single spark, but not being at once extinguished, he grew to a flame, and devastated the whole world. For their word eateth the body as a canker, and the rot in a single sheep infects the whole flock."

The maxim may be yet more fitly applied to the doctrine itself of the Judaisers, in the sense that a single error in the faith, such as that about the necessity of the law, overturns the whole faith. Chrysostom and Theophylact apply it, yet more particularly, to circumcision, the receipt of which acts like leaven, and corrupts the whole lump. Their application is supported by the fact that the Apostle, in vers. 2, 4, and 6, is treating of circumcision, and declares that he who is circumcised is debtor to the whole law. The Judaisers, however, seem to have persuaded the Galatians that circumcision was not a matter of great moment, and to have passed lightly over the onerous character of the burdens to which those who were circumcised subjected themselves. On the contrary, Paul here lays bare their artifice, and declares circumcision to denote a profession of the whole of the Jewish law, and to be a corruption of Christianity as a whole, on the ground that a little leaven leaveneth the whole lump.