(If ye go not forth) with your Prophet at the Battle of Tabuk (He will afflict you with a painful doom) in this world and in the Hereafter, (and will choose instead of you a folk other than you) who are better and more obedient than you. (Ye cannot harm Him all) i.e. by staying back you cannot harm Allah. (Allah is Able to do all things) whether it is punishment or reward.