Charles Ellicott Commentary Deuteronomy 29:18

"lest there should be among you man, or woman, or family, or tribe, whose heart turneth away this day from Jehovah our God, to go to serve the gods of those nations; lest there should be among you a root that beareth gall and wormwood;" — Deuteronomy 29:18 (ASV)

Lest there should be. —The connection with Deuteronomy 29:15 seems to be this: “I make this covenant binding with all your generations, in case there should even now be any root of idolatry among you which may grow up and bring forth fruit in later times, and bring a curse upon your whole country.” That there were such roots of idolatry is only too plain from Deuteronomy 31:16, and from what followed after the death of the elders of this generation. (Compare to Judges 2:10-12.)

A root that beareth gall and wormwood. —The same two words occur in Lamentations 3:19, and one of them (gall) in Psalm 69:21. From whatever root it came, there was One to whom it was given to drink. The Septuagint form of this expression, lest there is among you any root that springeth up in gall and bitterness, is incorporated into the warning in 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.