Matthew Poole and continuators on Galatians 5:9

9 A little leaven leaveneth the whole lump .

This is a proverbial expression, which (as others of that nature) is applicable in more cases than one. The Apostle made use of it, 1 Cor. 5.6. to perswade that Church to purge their Communion, by casting out the incestuous person: he maketh use of it here to perswade them to take heed of admitting any principles of false Doctrine, which he compareth to leaven, (as our Saviour does, Matth. 16.6, 12.) And that very fitly, both in regard of the sowre, and of the diffusive nature of it; the latter of which is here chiefly intended. The truths of God having such dependance one upon another, that he who erreth in any one Doctrine of Faith, seldom continueth long sound as to other points.