Второзаконие 13:9

To such persuasion Israel was not to yield, nor were they to spare the tempters. The accumulation of synonyms (pity, spare, conceal) serves to make the passage more emphatic. כּסּה, to cover, i.e., to keep secret, conceal. They were to put him to death without pity, viz., to stone him (cf. Lev 20:2). That the execution even in this case was to be carried out by the regular authorities, is evident from the words, "thy hand shall be first against him to put him to death, and the hand of all the people afterwards," which presuppose the judicial procedure prescribed in Deu 17:7, that the witnesses were to cast the first stones at the person condemned.

Moses is still upon that necessary subject concerning the peril of idolatry. In the close of the foregoing chapter he had cautioned them against the peril that might arise from their predecessors the Canaanites. In this chapter he cautions them against the rise of idolatry from among themselves; they must take heed lest any should draw them to idolatry, 1. By the pretence of prophecy (Deu 13:1-5). II. By the pretence of friendship and relation (Deu 13:6-11). III. By the pretence of numbers (Deu 13:12-18). But in all these cases the temptation must be resolutely resisted and the tempters punished and cut off.

13:9 Strike the first blow yourself: Because the guilty parties would be members of one’s own family (13:6), this difficult demand would test the depth of a person’s commitment to worship the Lord exclusively. Love for God must take priority over love for family members and friends (Matt 10:34-39).