Why Would God Command Parents to Kill Rebellious Children (Deuteronomy 21:19-21)?
I think in this one we have to take a step back for a moment, and to see that the covenantal structure that God has with his people ... God lays out the covenant law and says, "Here are the things which you must do to remain in covenant with me. If you do them, then I am obligated to pour out and lavish upon you all of the covenantal blessings." And you see those listed in Deuteronomy 28.
"But, vice versa, if you break he covenant law, then here are the covenant curses that I as a perfect, holy, just, and righteous God am obligated to now pour out upon you." The section in Deuteronomy 19 concerning the child, if you as a parent have a child who is continually transgressing and breaking the covenant law of God, you must remember that if you as a father were to harbor this child, and furthermore as a city, if the city harbored the child who was a continual covenant transgressor, then God is obligated, not just sitting back being mean, he's obligated to pour covenant curses out, not just upon you, but now upon the entire city. So, now when you think about that question, it goes back to the fact, do you love God more than you love all other things? Jesus Christ says this exact same thing in a different way in the New Testament when he says, "All who love child, mother, father, sister, brother, more than me, are not worthy of me." So, in other words, do we love God preeminently, or do we not? And if we make an idol out of anything, if we place anything above the living God, then we are harboring that which transgresses, and we cannot. He is worthy of our love, He is worthy of our devotion.