Hebrews 12:15

Heb. 12:15. Looking diligently lest any man fail of the grace of God; lest any root of bitterness springing up trouble (you), and thereby many be defiled;

In the sermon on "The Nature and End of Excommunication," Edwards cites this text to show that church members must testify against sin.

That the other members themselves may not be defiled, it is necessary that they bear a testimony against sin, by censuring it whenever it appears among them, especially in the grosser acts of wickedness. If they neglect so to do, they contract guilt by the very neglect; and not only so, but they expose themselves to learn the same vices which they tolerate in others; for "a little leaven leaveneth the whole lump." Hence that earnest caution of the apostle, Hebrews 12:15, "looking diligently, lest any man fail of the grace of God; lest any root of bitterness springing up, trouble you, and thereby many BE DEFILED."

Heb. 12:16