Yet another passage from my book on Islam for Mormons:
Islam is an absolutely rigorous, pure monotheism. “To God alone is true worship due,” declares the Qur’an. In this regard, it resembles Judaism rather more than Christianity. There is no God-man in Islam, no divine Son. A chasm separates man from God. Even the doctrine of the Trinity, with its claim that three persons are really one God, has never satisfied Muslim critics:
People of the Book, do not transgress the bounds of your religion. Speak nothing but the truth about God. The Messiah, Jesus the son of Mary, was no more than God’s Messenger and His Word which He conveyed to Mary: a spirit from Him. So believe in God and His Messengers and do not say: ‘Three.’ Forbear, and it shall be better for you. God is but one God. God forbid that He should have a son! … The Messiah does not disdain to be a servant of God, nor do the angels who are nearest to Him.
From a Latter-day Saint point of view, the Qur’an is crucially wrong on this important matter. Yet I have to confess that I have always found an amusing implication here. Many enemies of The Church of Jesus Christ of Latter-day Saints like to denounce us as polytheistic and therefore as non-Christian. They think that they escape the charge of polytheism themselves by simply declaring that the Father and the Son and the Holy Spirit are somehow, incomprehensibly, one. But the Muslims, whose mathematical abilities are historically well developed (as we shall see, they invented algebra), are not taken in by this. They have frequently denounced mainstream Christianity as polytheism. But it is not only Christians who are under the accusation of worshiping more than the one God. Even Jewish monotheism is suspect in the Qur’an.
 4:171-72. Note that the Qur’an seems to call Jesus God’s “Word” here, much as does the first chapter of the gospel of John. Thus, even though it rejects Christ’s divinity, the Qur’an retains an extraordinarily high and reverent view of him.
 9:30-31. Most Western scholars would say that the denunciation of Jewish polytheism here rests upon a misunderstanding, but it is possible that at least some of the Jews of Arabia held false doctrines. Certainly the Qur’an’s rebuke does not seem to apply to Judaism as we know it, either today or historically.