The Muslim approach to Comparative Religion is quite different from the Christian one.
The Christian is brought up to believe that his religion is the only true one along with Judaism which is a preparation for Christianity, and that all other religions are false. He thinks that God has chosen and set apart the children of Israel for the purpose of revealing His Messages and sending His prophets. And so, he believes only in the prophets and religious teachers of Israel and considers all other Prophets as impostors. Christian missionaries have all along employed their energies at proving the holy founders of other religions to be false and wicked men, so that they might establish the unique claim of Jesus Christ. One has only to read their books about the Prophet Muhammad (pbuh) and his Religion to find how their religious preconceptions and prejudices have made them incapable of seeing the truth of others. They have not hesitated even to mistranslate the Glorious Qur'an and spread many misstatements about the Prophet Muhammad (pbuh) to serve their own purpose. If they find anything in another religion resembling something in their own, instead of feeling happy, they feel discouraged and hasten to explain it away as due to Christian influence.
The Muslim, on the other hand, believes in the Divine Origin of all the Divine religions of the world. The Sacred Book of Islam declares that God has raised prophets in every nation to guide the people to the Path of Truth and Righteousness. Being the loving Creator and Sustainer of all the worlds, He cannot become partial and choose one nation to the exclusion of all others for revealing His Messages. A Muslim must believe in the prophets of all the Divine religions. He may feel sorry to see how Jews and Christians have in part forsaken and altered the true teachings of Moses and Jesus, but he can never speak against the prophets of their religions. For, he has
been directed by the Glorious Qur'an to respect and believe in them as true and righteous prophets of God as Prophet Muhammad (pbuh).
It is, therefore, with a feeling of deep love and respect for both Jesus and Muhammad (pbut), and for the religions which they preached, that I embark upon a comparative study of Islam and Christianity. If at times I find myself disagreeing with the Christians, it is not over the religion of Jesus, but over the altered shape and features that they developed after his departure. In the words of Lord Headley, "Islam and Christianity, as taught by Christ himself, are sister religions, only held apart by dogmas and technicalities which might very well be dispensed with."
 Lord Headley: A Western Awakening to Islam, p. 15.