Charles Spurgeon Commentary Hebrews 12:15

"looking carefully lest [there be] any man that falleth short of the grace of God; lest any root of bitterness springing up trouble [you], and thereby the many be defiled;" — Hebrews 12:15 (ASV)

Lest any root of bitterness springing up trouble you, and thereby many be defiled;

Sin is a bitter thing and a defiling thing. Unless we look diligently, it will grow in our hearts like the weeds grow in our gardens after a heavy rain, and it will spring up before we are aware of it.

Looking diligently lest any man fail of the grace of God;

Seeming to have grace, and yet not really having it