John Calvin Reformed @genevareformer

9 But thou shalt surely kill him. He would not that every one should privately execute vengeance without a public trial; but he referred to the ordinary custom, that the witnesses should throw the first stone at condemned criminals, as we shall see elsewhere.

Matthew Henry Presbyterian @wholebiblehenry

Further provision is made by this branch of the statute against receiving the infection of idolatry from those that are near and dear to us. I. It is the policy of the tempter to send his solicitations by the hand of those whom we love, whom we least suspect of any ill design upon us, and whom we are desirous to please and apt to conform ourselves to.

Commenting on Deuteronomy 13:6-11

John Gill Reformed Baptist @doctorgill

But thou shalt surely kill him,.... Not privately and secretly, when and where he entices, nor the enticed himself by his own authority, but after being examined, judged, and condemned by the civil magistrate; and none might judge a false prophet but the sanhedrim at Jerusalem, the sanhedrim of seventy one (m); see Luk 13:33, but the difficulty is how such an one could be...