Why

I saw on a wall, in the street of religion an inscription which Reads "So when you meet those who disbelieve, smite necks till when you have killed and wounded many of them, bind a bond firmly thereafter either for generosity or ransom until the wars lays down its burden. thus ordered by Allah to continue in carrying out Jihard against the disbelievers. till they embrace Islam and are saved from punishment in the Hell-fire. but if it had been Allah's will, he himself could certainly have punished them " When i was done with reading the epitaph I said to myself Why?