This is the best way to explain Islam: It is the revenge of Middle Eastern Christians and Jews for the Hellenization and Romanization of the biblical religious tradition. Islam became a way to remain biblical without accepting all the pagan additions to the biblical tradition that came from the gentile Christian churches, like the divinity of Jesus, the Trinity, and all that stuff. When the Muslims arrived in Egypt and Syria, the Christians there (and some Jews) who had been persecuted by the Orthodox Christian imperial church willingly accepted Islam. Jews who were also persecuted by Byzantine rulers welcomed the Muslims and sometimes converted. Islam is in many ways more biblical than either orthodox Christianity or Talmudic Judaism; both reinterpreted the old religion of Israel in an undesirable way.
In Response to: Explaining Islam: What I Wish You Knew