Deuteronomy 13:9

you shall not consent to them, nor hearken to him, neither shall your eye spare him or have compassion, nor shall you hide him in secret;

do not assent to him in your heart’s belief.

nor accept his words in action.

you must not spare him from being killed.

you must not cover him by refraining from action. Rather, you must reveal the matter, so that witnesses will come and hear it from his own mouth (for so it is written [17: 6]) — and then you must kill him.

THOU SHALT NOT ‘THOVEH LO’ — “you shall not ‘long’ for him, nor shall you love him. Because it is said, Thou shalt love thy neighbor as thyself — [it is necessary to caution that] this one [who seeks to mislead you into idolatry] you shall not love.” This is Rashi’s language quoting the Sifre. 89. But in the Gemara the Rabbis have said [in connection with this verse]: “But [if the one misled] avah (wanted) and consented [to the words of the inciter, although he actually did not worship the idols, the misleader] is guilty” [thus showing that the word thoveh is not an expression of “longing” as Rashi holds, but of “willingness”]. And this is correct, for avah is an expression of “desire,” as it is said, And the Eternal thy G-d was not ‘avah’ (willing) to hearken unto Balaam, meaning “He did not desire.” So also, he is not ‘avah’ (willing) to perform the duty of my husband’s brother,, 25:7. [this expression being based upon the statement in the first part of that verse], and if the man ‘desires’ not to take his brother’s wife. Thus, thou shalt not ‘thoveh lo’ means [“thou shalt not be willing] in your heart [to give credence to him”], nor hearken unto him by consenting to him, saying “I will do so; I will go and I will worship the idol you mentioned.” And [the inciter] becomes liable to the death penalty because of his [the victim’s] consent. And such is the opinion of Onkelos [who translated]: “Do not accept [the offer] from him.” Now these two prohibitions [Thou shalt not be willing to give credence to him in your heart, nor shalt thou hearken unto him] are like Neither shalt thou desire thy neighbor’s house [which prohibits us from desiring what belongs to another], and Thou shalt not covet thy neighbor’s house [which prohibits us from scheming to acquire it], so that if he desires it in his heart, he infringes the first prohibition, and if he goes on to do as he thought, he transgresses also the second negative commandment.

NEITHER SHALL THINE EYE PITY HIM — to show him mercy that he not die.

NEITHER SHALT THOU SPARE because of the close [family] relationship as mentioned, as it is said, as a man spareth his own son that serveth him.

לא תאבה לו, when he suggests that you investigate the truth of his words that a certain form of idolatry is demonstrably effective for its believers, do not assent to listen to him.

ולא תשמע אליו, you must not listen to him to make such an experiment, and to go through a “conditional” obeisance as a test. The reason is that the moment you even entertain doubts about the utter falsity of what the seducer claims, in the end you will become a victim of his persuasiveness. You could not even entertain any doubt about G’d and His Torah unless you had never properly understood the greatness of G’d and His mastery in the universe.