In the parsha Moshe Rabeinu speaks to all of Bnei Yisrael to set up a covenant and an oath of a curse if they do not keep the covenant. The passuk states (יז) פן יש בכם שרש פרה ראש ולענה, “maybe there will be amongst you root flourishing bitter herbs.” What does a person have to do with do bitter herbs, and how does this effect a covenant?
Onkelos translates these words as: Maybe there will be amongst you a man who thinks about sinning by accident or on purpose. The Nesina LaGer explains that the thoughts of a person are compared to a root which produces growths. If the root is sweet, it will grow sweet herbs, and if it is bitter, it will grow bitter and poisonous herbs. So too is with the thoughts of a person, if he thinks about aveiros, it will cause him to act upon his thoughts and sin. The Me’at Tzari adds that the lashon of הרהור, thoughts, is from the lashon of הריון, conceive. The thoughts of a person produce and create what a person says and does. The Torah warns, maybe there will be amongst you a person who will think to sin, therefore you are being brought into this covenant with an oath.
The Ramban explains that this passuk includes even a person who is not actually at the covenant, as it states (in passuk יד) ואת אשר איננו פה עמנו היום “and also that who is not here with us today.” A bitter root, with time, will produce poisonous herbs, which is a parable for a father and a son. A father is like a root with which a son is created and flourishes from. A sweet root will not produce a bitter herb. So too anyone whose heart is complete with Hashem and does not think about idolatry, will not give birth to children that will admit to idolatry. Just as the sweet root produces only sweet herbs, so too the children inherit the genes of the parents and follow in their footsteps, being dedicated to Hashem Who is one. Everyone who was at the covenant included their future generations which will be produced from their roots.
Similarly we find people who return to the truth and reconnect to Hashem and His mitzvos, although they were completely lost. How is this, what is their zechus? I heard from Mori V’Rebbi HaRav Yaakov Friedman shlit”a that this is because their alta bubbies davened when they lit Shabbos candles, for their children to follow the path of Hashem. Their feeling towards Yiddishkeit was passed down into the being of their descendants which helped motivate them and bring them back to the truth.
May Hashem help us direct our thoughts to be completely dedicated to Hashem and produce sweet fruit- proper actions and descendants.