John Piper Says Christians Should Not Own Guns But The Reason Why is Not Even Biblical

John Piper says Christians should not own guns. He then says that if I Christian has someone break in to their home and they kill them they might go to hell. Well, that is odd coming from Calvinist John Piper that says he believes in predestination. If a man breaks into your home to harm you, or your family, and you defend yourself, and your family, with a gun and the man dies and goes to hell then guess what? The man was not predestined to go to heaven. Why is it that Piper's theology does not work in real life on this issue?