O’ Mohammad, if it was an easy campaign, they would have been quite ready to follow you. However, they could not handle the situation (marching a long way in the desert in the hot summer, not having enough time to harvest their new crop and going to face the strong Roman empire’s army.) They would dare to swear by God and say: “If we could, we would certainly join you.” By saying such lies, they are destroying their own souls. God knows that they are liars.