신명기 13:10 해설: Rashi, Ibn Ezra, Rashbam & Rabbeinu Bahya

כי הרג תהרגנו BUT THOU SHALT SURELY KILL HIM — and if he has left the court after having been acquitted have him brought back for condemnation if you know anything against him; if, on the other hand, he has left the court after being found guilty do not bring him back to plead in his favour (Sifrei Devarim 89:6-7).

Let your hand be first Were it not for the tradition, it would seem that this is addressed to each one of the witnesses [cf. 17: 7] [the halakha [Sanhedrin 67a] is that it is the witnesses who begin the stoning, not the people subjected to the enticement, whenever they are distinct from one another — Translator].

כי הרג תהרגנו, the word כי means אלא, but, i.e. but be sure to execute him.

ידך תהיה בו בראשונה THINE HAND SHALL BE FIRST UPON HIM [TO PUT HIM TO DEATH] — He who was to be seduced to idolatry has the duty to put him to death; if he did not die by his hand he must die by the hands of others, as it goes on to state “and afterwards the hands of all the people” (cf. Sifrei Devarim 89:8).