Deutéronome 29:17

Beware, then, lest there be among you now or hereafter a man, woman, family, or tribe, whose heart may be turned away to wander any day from the service of the Lord our God to worship the idols of those nations; or lest there be among you the error which striketh root (in them) whose heart wandereth after his sin; for the beginning of sin may be sweet, but its end is bitter as the deadly wormwood;

developing into hemlock and wormwood Hemlock is harmful to someone who is healthy, and the illnesses that it produces are among the deadliest.

LEST THERE SHOULD BE AMONG YOU etc. “Therefore, I must place you under an oath.” Thus far is Rashi’s language. He has commented well. And the purport thereof is to state, “I must bring you now into this covenant with an imprecation and an oath on account of my fear that perhaps the hearts of some of you have been beguiled into following the abominations of Egypt as you did at the [affair of the golden] calf, or the abominations of Ammon and Moab that you saw on the road when you had the affair with Baal-peor,” for at the first covenant at the time of the Giving of the Torah there were no imprecations and curses. He stated [lest there should be among you] man or woman because a woman is frivolous [and can easily be led into idol-worship]. He stated a similar expression in [the chapter dealing with an individual] worshipping the idols. He mentioned individuals, family, and tribe [lest there should be among you man, or woman, or family, or tribe] meaning a multitude, but he did not say it [lest they should worship the idols] concerning all of them, out of respect [to them]. Or it may be that it was impossible for the hearts of all of them to turn to the idols on that day, because, if so, they would not have come into the covenant of G-d and His oath, for who could have compelled them. A family or tribe, however, might have come into the covenant for fear of the majority. He stated lest there should be among you [man, or woman etc.] whose heart turneth away this day referring to him who has already been beguiled to idol-worship and who secretly believes in them that day. Or lest there should be among you an evil root that will blossom and grow and in the coming days will bring forth poisonous buds and grow bitter herbs. This refers back to him that is not here with us this day, for the father is the root and the son is the twig that shall grow forth out of his roots. He mentioned the root in order to state that he can bring the coming generations into this oath, for the root from which the coming generations will grow is before him this day, and it comes within this covenant and oath. He stated a root that beareth gall to suggest that from a sweet root no bitter plant will issue, and that all those whose hearts are perfect with the Glorious Name and gave no thought to the idols, will not give birth to a child, who will avow idolatry. Now, do not refute me in this matter on the basis of the verse If he [a man who is just, and does that which is lawful and right] beget a son that is a robber, for the matter is true, there being a great secret therein which I cannot explain.

איש או אשה, neither a man nor a woman who would seduce you to follow the vain pursuits of the nations with whom you will be living in close proximity, and who might be the cause that you would default on the undertakings in this covenant. This is the reason I have insisted that all of you be present at this ceremony, seeing that G’d examines hearts He will know who only pays lip service to this covenant and who is sincere about it. You will not be able to deceive Him.

פן יש בכם שורש פורה ראש ולענה, a simile for people planning to beguile the multitude to adopt their own idolatrous beliefs.

פן יש בכם, “lest there be amongst you, etc.;” this is an additional reason for renewing the original covenants.

אשר לבבו פונה היום, “whose heart is even now turning away, etc.;” he will entertain the thought of abandoning G–d and His Torah. Moses is frank, admitting that there is cause for worry. Furthermore,

פן יש בכם שורש פורה ראש ולענה, “lest there is perchance amongst you a stock sprouting poison weed and wormwood.” In what follows, Moses goes into greater detail about what he is worried about.