John Knox, Appellation, on Deuteronomy 13 [emphasis added; please see note below]:
“To the carnal man this may seem to be a rigorous and severe judgment, than even the infants there should be appointed to the cruel death; and as concerning the city, and spoil of the same, man’s reason cannot think but that it might have been better bestowed, than to be consumed. But in such cases, let all creatures stoop, and desist from reasoning, when commandment is given to execute his judgment. I will search no other reasons, than the Holy Ghost hath assigned; first, That all Israel should fear to commit the like abomination; and, secondly, That the Lord might turn from the fury of his anger: which plainly doth signify, that, by the defection and idolatry of a few, God’s wrath is kindled against the whole, which is never quenched, till such punishment be taken upon the offenders, that whatsoever served them in their idolatry be brought to destruction, etc.”
Note: I add this explanation because there is so little understanding today of Christian theology and the relationship between the Old and New Testaments and hermeneutics in general. This passage is dealing with the theocratic nation of ancient Israel and the requirement to destroy idolaters living in their nation. It is not a call for vigilante justice on the part of modern-day Christians to go out and kill unbelievers. The New Testament teaches that things that happened of old were for our instruction and example (1 Corinthians 10:11: “Now all these things happened unto them for ensamples: and they are written for our admonition, upon whom the ends of the world are come.”). The above commentary is highlighting a principle that still applies today; namely, that God does not smile on idolatry and holds nations accountable for its practice and toleration. However, the modern means by which idolatry is addressed, ie. preaching the Gospel, etc., differ from those required in the ancient theocracy. Protestantism does not teach the burning of heretics or any of the other atrocities that have been committed in Christ’s name in the past. At the same time, though, we must warn our fellow citizens that God does hate idolatry and that He does bring judgment upon nations that practice it. Whether or not our fellow citizens choose to listen to this warning is up to them.