Lest there should be; or take heed or beware lest there be; for it seems to be an ellipsis, or defect of a verb, which is usual in Scripture, and which we have in a case parallel to this. Genesis 3:22. And now we must take care lest he put forth, &c. Or this particle lest may be joined with Deuteronomy 29:14,15, to this purpose, I now renew the covenant with you, and with your posterity, lest any of you or yours should be tempted to depart from God, &c. Whose heart turneth away, i.e. who turneth away from God to idols, not by constraint, but by choice, and the inclination of his own heart. By this phrase he leads them to the spring of their sin and ruin, even their own hearts, which he admonisheth them hereby to look to above all things. A root; either,
1. An evil heart inclining you to such cursed idolatry, and bringing forth bitter fruits. Or rather,
2. Some secret and subtle apostate, who lurks and works like a root under ground, and slyly conveys his poison to the infection of others; for both the foregoing and following words speak of some particular person. Gall and wormwood, i.e. which though for the present it may please your fancy, yet in the end, assure yourselves, will produce bitter fruits, not only distasteful to God, but also poisonful and destructive to yourselves.