Most college students ask, ‘If there is only one God, why are there so many religions?’ A question I as a Rabbi have often been asked. My answer is that Allah could have made all of us monotheists, a single religious community, but (didn’t) in order to test our commitment to the religion each of us have been given by God. 
“If Allah had so willed, He would have made you a single people, but (God’s plan is) to test you in what He has given you: so compete in all virtues as in a race. The goal of you all is to (please) Allah who will show you (on judgment day) the truth of the matters in which you dispute.”  (Qur’an 5:48)
This means religious pluralism is the will of God. Yet for centuries most believers in one God have depreciated each other’s religion, and some believers even resorted to forced conversions, expulsions and inquisitions. Yet all monotheists pray to the same God, and all prophets of monotheistic faiths are inspired by the same God. 
How did this intolerance start, and how can we eliminate religious intolerance from the Abrahamic religions? 
Greek philosophy, with its requirement that truth must be unchanging and universal, influenced most teachers of sacred scripture during Medieval times to believe that religion was a zero sum game; the more truth I find in your scripture the less truth there is in mine. 
Instead of understanding differing texts as complementary, they made them contradictory and declared the other religion’s sacred text to be full of errors.
If religion is to promote peace in our pluralistic world we must reject the zero sum game ideology and develop the pluralistic teachings that already exist within our sacred scriptures. 
All prophets are brothers. They have the same father (God) but different mothers (mother tongues, motherlands and unique historical circumstances that account for all the differences in their scriptures.
Note that the Arabic word umm for mother derives from the same root as the word ummah: their mother people and their mother tongue. “Prophets are brothers in faith, having different mothers. Their religion however; is one“.  (Hadith: Muslim, Book #030, Hadith #5836) 
I am a Reform Rabbi who first became interested in Islam when I studied it at the Hebrew University in Jerusalem 60 years ago. I continued my study of Islam off and on for many years; and for some time I have considered myself to be a Reform Rabbi and a Muslim Jew.
I am a Muslim Jew ie a faithful Jew submitting to the will of the one God, because I am a Reform Rabbi. As a Rabbi I am faithful to the covenant that God made with Abraham (a), the first  Jew to become a Muslim, and I submit to the commandments and the covenant God made with the people of Israel at Mount Sinai. 
As a Reform Rabbi I believe that we should not make religion difficult for people to practice.
This lesson Prophet Muhammad (s) taught 12 centuries before the rise of Reform Judaism in the early 19th century. Most statements in the Qur’an about Orthodox Jewish beliefs, and Ahadith relating Muhammad’s (s) comments about Orthodox Judaism, prefigure the thinking of Reform Rabbis some 12-13 centuries later.
As the Qur’an tells us (17:110) “Say, call upon Allah or call upon Ar-Rahman, the Most Merciful. Whichever [name] you call – to Him belong the best names.” And do not recite your prayer [too] loudly or [too] quietly, but seek a way in between [moderation].”
This ayah is a basis of Reform Judaism. God has many names because God has a complex personality; but also because different people and different peoples/tribes/nations relate to the one God in different ways.
Thus no one should raise his voice in prayer over others as though his prayers were better than those of others in his own community; or in other monotheistic communities.