Allah (ta’ala) said, {They thought that their fortresses would protect them from Allah but Allah came upon them from where they had not expected, and He cast terror into their hearts so they destroyed their houses by their own hands and the hands of the believers. So take warning, O people of vision} [Al-Hashr:2].

In the wake of the terrorist attacks of September 11, 2001, much of the analysis focused on the possible motives of Islamic radicals, and almost all of it was prefaced with four simple words: “They hate us because . . . ” What came after those words varied, but invariably it told us more about the speaker than about Mohamed Atta and his allies, or Al Qaeda, or insurgent Muslims around the world generally: “we are rich”; “we are free”; “we are advanced [socially|culturally|politically|economically|morally].” What none of the analysts ever said, not because they were trying to hide the truth but more likely because it never occurred to them, was that “They hate us because we are Christian.”

Yet that is the reality which lies behind Islamic aggression today. That we aren’t Christian—no longer, or at least not really—makes no difference; the perception among Muslims so committed to their faith and to the traditional understanding of jihad that they will sacrifice their lives in the...