With Mohammed all of the many kinds of heresy were combined into one new religion. Can we not see at least an echo, if not a fulfillment, of I John 2:18? "Little children, it is the last time: and as ye have heard that antichrist shall come, even now are there many antichrists; whereby we know that it is the last time."
Who is this one antichrist that sums up the work of all the heretics who had come before, be they Legalists, Gnostics or Arians? Be they Montanists with a "new prophecy" or Pneumatamachoi that deny the Holy Spirit? All of these antichrists had the system of their doctrine swept up into the substance of Islam by the antichrist himself, who I have long identified as that raider who came out of the desert to convert the cities and cultures of Middle Eastern Christianity into an extension of the desert, a place of barrenness.
Be sure to read more by Fr. Hart at The Continuum.