How important is it that we worship God and him alone? Deuteronomy 13:6-11 is one of those passages that jars our modern sensibilities as a stark reminder that God will not be trifled with:
 “If your brother, the son of your mother, or your son or your daughter or the wife you embrace or your friend who is as your own soul entices you secretly, saying, ‘Let us go and serve other gods,’ which neither you nor your fathers have known,  some of the gods of the peoples who are around you, whether near you or far off from you, from the one end of the earth to the other,  you shall not yield to him or listen to him, nor shall your eye pity him, nor shall you spare him, nor shall you conceal him.  But you shall kill him. Your hand shall be first against him to put him to death, and afterward the hand of all the people.  You shall stone him to death with stones, because he sought to draw you away from the LORD your God, who brought you out of the land of Egypt, out of the house of slavery.  And all Israel shall hear and fear and never again do any such wickedness as this among you. [ESV]
God is jealous for his worship. The passage continues to lay similar methods of dealing with apostate cities.* The children were to be militant about their devotion to the Lord, not even sparing their own family members when they turned away from the worship of the Lord God. There was to be no pity in Israel’s theocracy for those who would attempt to “draw you away from the Lord your God, who brought you ought of the land of Egypt.” And why should there be? God had graciously delivered them from slavery and then shown them continued mercy and faithfulness throughout their sojourn in the wilderness en route to Canaan.
I am not theonomist, and I do not believe that Christians have the authority either politically or, most important, biblically through the lordship of Christ, to stone those who depart from their God. But I still believe there is a very important lesson in this passage, and one that pertains to us here and now: we should take God and our worship of him very seriously. We should be characterized by a whole-hearted, unflinching devotion to our God, and to the best expression of this “radical monotheism,” the public worship of God in our local assemblies. We should not turn away, and we should realize that all those who have turned aside from the one true and living God as revealed in Jesus Christ are in grave danger of eternal condemnation. God hates idolatry and infidelity. He is a jealous God. He will not be trifled with.
In this era where we sit under the shadow of the revelation of Jesus Christ and his authoritative teaching given to us in the gospels and writings of the apostles, God has not relaxed or changed his mind as to the centrality and indispensability of our worshipping him alone. No, he has not changed at all. And this should move us who are believers to give thanks to God that he has graciously worked in us to embrace Jesus Christ, become true worshippers of God, and thus escape his wrath. It should move us to be serious about corporate worship, our public expression of our devotion to God amidst like-minded believers. And it should move us to seek earnestly to rescue the numerous idolaters through the proclamation of the gospel of Jesus Christ.
*Lest we assume that these commands were a sign of a barbarous primitive religion, I think it is worth noting that such an argument betrays an assumption that this passage is not inspired by God and that our God is really not as important and glorious as such passages reveal. Moreover, such an argument ignores the way the passage itself urges the people not to follow their impulse to show mercy to the idolaters. Simply put, for the children of Israel to love their family more than God is damnable sentimentality, just as it is for us who follow Jesus Christ (cf. Luke 14:26).