if you do not migrate he will afflict you with a painful punishment and bring other people in your stead and you will not be able to harm him in the least and allah is able to do all things.
إلا تنفروا يعذبكم عذابا أليما ويستبدل قوما غيركم ولا تضروه شيئا والله على كل شيء قدير