See Foot note [(30)] p. 30.
Compare the Bhagvat Gita, iv. 7-8:—
"Whenever there is decay of righteousness, O Bharata, and there is exaltation of unrighteousness, then I myself come forth;
For the protection of the good, for the destruction of evil-doers, for the sake of firmly establishing righteousness, I am born from age to age."
The words italicised suggest the Hindu doctrine of Incarnation and Metempsychosis. Orthodox Muslims do not believe in any such doctrine (حلول و اتحاد) but would substitute for the italics the words: I send a messenger or reformer. See, e.g., Quran, xvi. 36.
To students of Islam and its history I cannot recommend better and more useful books than the Rt. Hon. Dr. Syed Ameer Ali's Spirit of Islam and History of the Saracens. New and revised editions have been recently published. They present the various aspects of Islam in their proper perspective. They are classics for English readers.
"Grant the existence of God and it is impossible to deny that Muhammad was His Messenger. A man does not change the belief of half the world by chance." So wrote a Christian friend of mine.