Not to refrain from incriminating him

This mitzvah forbids concealing testimony or withholding information that would incriminate a mesit (missionary to idolatry). Normally, Jewish law encourages restraint in capital cases to protect the accused. However, in the case of the enticer, the Torah commands the opposite — ensuring that his crime is exposed and punished. Concealing his actions would protect a danger to the community and undermine Hashem’s covenant.

Commentary & Classical Explanation:

• Rambam (Hilchot Avodat Kochavim 5:4): One must not hold back evidence against the mesit, since his enticement undermines the very foundation of Israel’s faith.
• Sefer HaChinuch (Mitzvah 467): The root is to safeguard belief in Hashem by removing those who attempt to corrupt it.
• Talmud (Sanhedrin 67a): Unlike other defendants, here the Torah requires active participation in his conviction, ensuring idolatry gains no foothold.