13:3
If the person is leading people away to worship false gods, then they must be ignored. The accuracy or otherwise of their prophecies is neither here nor there. Worshipping God, and having no other gods is the primary point. Also, the greatest commandment is to worship the Lord with all that we have. As it says here, “The Lord your God is testing you”. So we see that even the false prophet is acting within the sovereignty of God. Now why is “God testing you”? Surely He knows whether or not our faith is genuine? Various reasons can be given. One is that it is for our own benefit. It enables us to know where we truly stand, it also lets others know where we stand. Also, coming through the test can strengthen us.
13:4
“It is the Lord your God you must follow”. God must be above all. So how do we do this practically? We are to keep His commands and obey Him. We should also note that Jesus considered obedience to be of paramount importance, and the true sign of whether or not we love Him. We are to serve Him, so we live our lives to do His will. We are to hold fast to Him. So when faced with extreme pressure we look to God, not to idols, for help.