…do not heed him… (Deuteronomy 13:9)
In the previous mitzvah, we said that we are not to befriend the meisis, one who tries to lure other Jews to idolatry. Our current mitzvah prohibits softening our position on the meisis. We are not to give him the opportunity to try to sway us with his point of view. We must stand firm in this matter.
One might think that one shouldn’t be so harsh towards the meisis since, generally speaking, we should try to reduce the animosity between ourselves and our enemies (see Exodus 23:5 and Targum Onkelos there). This mitzvah tells us otherwise: when it comes to the meisis, we are to hold our ground and not budge one iota.
The reason for this mitzvah is as we have said: we are obligated to take a hard line against idolatry. To provide idolatry with even a small entryway goes counter to our missions as Jews.
This mitzvah applies in all times and places. It is discussed in the Talmud in tractate Sanhedrin on pages 29a, 33b, 67a and 85b. It is codified the Mishneh Torah in the fifth chapter of Hilchos Avodas Kochavim. This mitzvah is #18 of the 365 negative mitzvos in the Rambam’s Sefer HaMitzvos and #25 of the 194 negative mitzvos that can be observed today as listed in the Sefer HaMitzvos HaKatzar of the Chofetz Chaim.