I have not read the Unpanishads or the Baghavad Gita, two ancient classics of Indian scripture that are considered sacred to Hindus. I have not read the Granth Sahib that is the sacred book of Sikhism, which incidentally is a monotheistic religion. Neither have I studied the teachings of the Buddha in any detail. I have not read the New Testament that is sacred to Christians, nor have I studied the Koran. One thing that is common between Judaism and Islam is that the founding documents, the Torah (The Five Books of Moses, the Bible) were supposed to have been dictated by God to Moses, while the Koran was supposed to have been dictated by God to Mohammed. Since both are monotheistic religions it was presumably the same God, so why did he need to dictate his thoughts/ commandments to two different prophets so far apart in time. That is a mystery. In all of this I suppose that my level of knowledge and experience is about that of any reasonably well-educated secular person, and indeed of most Bible Scholars, who probably have never cracked the sacred books of any other religion.
The question then arises, which of these sacred books are really sacred, or are they all not sacred. I cannot legitimately see that all of them can be sacred, after all if one of them is really the real thing, why have not the adherents of the non-legitimate religions have transferred to that. Wouldn’t it be obvious? Of course, that is what each of the proselytizing religions, particularly Christianity and Islam claim, both of them deriving legitimacy from Judaism, but both of them denigrating their source religion and in order to claim the mantle of “chosenness” actually trying to kill all Jews and stamp out their religion. Then Christianity and Islam fought wars over many centuries for supremacy.
Now many years later, most of the Western Christian countries have become secular and the Church has lost its control over them. Whereas in the Muslim world, where there is no tradition of separation of Church and State, they are still fighting this battle and this is going to be a protracted and bloody internal war. Already the lines are drawn, not only between Sunni Islam and its heretical Shia sect, but also between normative traditional Islam, such as practiced in Saudi Arabia and Egypt and the so-called Islamic State, that purports to be the real thing. They are the ones that claim that God/Allah has told them to go out and kill all infidels, including all Jews, Christians, Hindus, Buddhists, Yazidis, Kurds, Shia and non-IS Sunnis, and to establish a new Caliphate to cover first all of the Middle East and much of Europe and Asia, and then of course, the whole world. Since they are beyond rational appeal and since they are now taking the fight to the enemy, i.e., terrorism in Europe and the US, they will have to be stopped and the only way is militarily, by war. So much for comparative religion.