But the central point where this new heresy [Islam] struck home with a mortal blow against Catholic tradition was a full denial of the Incarnation.
Mohammed did not merely take the first steps toward that denial, as the Arians and their followers had done; he advanced a clear affirmation, full and complete, against the whole doctrine of an incarnate God. He taught that Our Lord was the greatest of all the prophets, but still only a prophet: a man like other men. He eliminated the Trinity altogether.
With that denial of the Incarnation went the whole sacramental structure. He refused to know anything of the Eucharist, with its Real Presence; he stopped the sacrifice of the Mass, and therefore the institution of a special priesthood. In other words, he, like so many other lesser heresiarchs, founded his heresy on simplification.
~Hilaire Belloc: The Great Heresies, Chap. III.
Continue reading Chapter III. The Great and Enduring Heresy of Mohammed