According to Sir William Muir, Marcus Dods, and some others, Mohammed was at first sincere, but later, carried away by success, he practised deception wherever it would gain his end. Koelle "finds the key to the first period of Mohammed's life in Khadija, his first wife", after whose death he became a prey to his evil passions [Demonstated by his repeated rape of his nine year old 'wife' -- my comment].
Sprenger attributes the alleged revelations to epileptic fits, or to "a paroxysm of cataleptic insanity".
Zwemer himself goes on to criticize the life of Mohammed by the standards, first, of the Old and New Testaments, both of which Mohammed acknowledged as Divine revelation; second, by the pagan morality of his Arabian compatriots; lastly, by the new law of which he pretended to be the "divinely appointed medium and custodian". According to this author, the prophet was false even to the ethical traditions of the idolatrous brigands among whom he lived, and grossly violated the easy sexual morality of his own system. After this, it is hardly necessary to say that, in Zwemer's opinion, Mohammed fell very far short of the most elementary requirements of Scriptural morality. Quoting Johnstone, Zwemer concludes by remarking that the judgment of these modern scholars, however harsh, rests on evidence which "comes all from the lips and the pens of his own devoted adherents. . . And the followers of the prophet can scarcely complain if, even on such evidence, the verdict of history goes against him".
"Cataleptic insanity" ... and demonic possession sums up the true nature Mohammed and Islam in my view.