Galatians 5:9 - Commentary Critical and Explanatory on the Whole Bible

A little leaven leaveneth the whole lump. A little leaven - the false teaching of the Judaizers. A little legalism, mixed with the Gospel, corrupts its purity. To add ordinances and works in the least degree to justification by faith, is to undermine 'the whole.' So "leaven," false doctrines (Matthew 16:12; cf. Matthew 13:33). In 1 Corinthians 5:6 it means the corrupting influence of one bad person; so Bengel refers it here to the person (Galatians 5:7-8; Galatians 5:10) who misled them (Ecclesiastes 9:18; 1 Corinthians 15:33). False doctrine answers better to "persuasion" (Galatians 5:8).