إِلاَّ تَنفِرُواْ يُعَذِّبْكُمْ عَذَابًا أَلِيمًاIf you march not forth, He will punish you with a painful torment,Ibn Abbas said,"Allah's Messenger called some Arabs to mobilize, but they lagged behind and Allah withheld rain from coming down on them, and this was their torment."Allah said,وَيَسْتَبْدِلْ قَوْمًا غَيْرَكُمْand will replace you by another people,who will give aid to His Prophet and establish his religion. Allah said in another Ayah,الْفُقَرَاءُ وَإِن تَتَوَلَّوْاْ يَسْتَبْدِلْ قَوْماً غَيْرَكُمْ ثُمَّ لَا يَكُونُواْAnd if you turn away (from the obedience to Allah), He will exchange you for some other people and they will not be your likes. (47:38)وَلَا تَضُرُّوهُ شَيْيًاand you cannot harm Him at all,you can never harm Allah when you lag behind and stay away from joining Jihad,وَاللّهُ عَلَى كُلِّ شَيْءٍ قَدِيرٌand Allah is able to do all things.He is able to destroy the enemies without your help