I have asked myself this question regarding Islam and Judaism, as well as Islam and Christianity, for an uncountable number of years. But it is only now, very recently, that I believe that I finally understand the answer to your question. After all is said and done, the answer is a very clear and simple one, so simple that I should have seen it years ago. But then, the East and the West are two different consciousnesses; and it takes a while to develop a double consciousness. And, of course, others might have other responses for you.
The Qur’an was given by Heaven to mankind through a prophet, who was called to be a messenger of Allah’s Divine Discourse. Hence, Islam begins with a very special human being, made special by Allah’s anointing attention. We are called upon, therefore, not only to understand the capabilities of human nature through the example of a prophet, but also the nature and character of the human being of prophecy.
Through Islam, Allah has given us the Seal of Rasuls. So we need to pay special attention to that last experience offered us. Is it no wonder that those who denigrate Islam and Muslims often do so by denigrating the Prophet first? (May Peace and Blessings Be Upon Him Forever.)
Judaism also has had prophets, so we are told. But we are faced with two different telling: the biblical one as found in the Jewish texts (The Hebrew Bible and the Talmud) and the Islamic one as found in the Qur’an.
And when we examine the Jewish prophets as portrayed in the Hebrew bible in light of how the Qur’an presents prophets to us, we must unabashedly conclude that the two religions teach us two mutually exclusive versions of who prophets are as human beings and what a prophet’s behavior has been like in the world. We are then pulled immediately back to the Quranic Surahs that inform us that the Jewish texts have been altered, which, once you read the Jewish narratives, must mean fictionalized for ethnocentric purposes.
Would a prophet--* a real prophet *--do what Lot does in the Jewish narratives? Would a real prophet arrange for a certain general to be killed so that he might have the man’s wife for himself, as David does in the Jewish texts? Would a real prophet use the basest of sexual language to describe a sinful and idolatrous nation as Ezekiel does in the Jewish texts?
You must remember that a prophet is someone through whom Allah’s word passes. To say that a real prophet would act the way many of the so-called Jewish prophets have acted amounts to saying that Allah acts in that manner. Hence, the Muslim must conclude that the Jewish texts, ultimately, are not "the word of God."