Religious ideas and practices take root not because they are promoted by forceful theologians, nor because they can be shown to have a sound historic… - Karen Armstrong

Ibn al-Arabi gave this advice:
Do not attach yourself to any particular creed exclusively, so that you may disbelieve all the rest; otherwise you will lose much good, nay, you will fail to recognize the real truth of the matter. God, the omnipresent and omnipotent, is not limited by any one creed, for he says, 'Wheresoever ye turn, there is the face of Allah' (Koran 2:109). Everyone praises what he believes; his god is his own creature, and in praising it he praises himself. Consequently, he blames the disbelief of others, which he would not do if he were just, but his dislike is based on ignorance.

As an inspiration for terrorism, however, nationalism has been far more productive than religion. Terrorism experts agree that the denial of a people’s right to national self-determination and the occupation of its homeland by foreign forces has historically been the most powerful recruiting agent of terrorist organizations, whether their ideology is religious (the Lebanese Shii) or secular (the PLO).

The Qur’an had begun to develop a primitive just war theory. In the steppes, aggressive warfare was praiseworthy; but in the Qur’an, self-defense was the only possible justification for hostilities and the preemptive strike was condemned.5 War was always a terrible evil, but it was sometimes necessary in order to preserve decent values, such as freedom of worship. Even here, the Qur’an did not abandon its pluralism: synagogues and churches as well as mosques should be protected. The Muslims felt that they had suffered a fearful assault; their expulsion from Mecca was an act that had no justification. Exile from the tribe violated the deepest sanction of Arabia; it had attacked the core of the Muslims’ identity.