It can be shown using a metaphysical argument that there exist a pre-eternal bridge between Islam and Christianity. Metaphysics recognizes that while we are creatures that currently exist within a condition of time, that time itself is ultimately an illusion. Incidentally, this can also be shown by a simple spiritual interpretation of Einstein's theory of relativity.
In the Holy Quran, there is a covenant known as the covenant of Alast. It is found in Surah 7, verse 171. Allah is questioning all souls before the beginning of time in the pre-eternal dawn, "Am I not your Lord?" The covenant was established when all souls answered Allah testifying that He indeed was.
When we extract time out of the situation, then in the case of Christianity, this means that the truth of the historical Christ must be the truth of all Christians; all Christians at their very core are in fact the Christ that was begotten before time began. This is also consistent with the teaching in A Course in Miracles (Text p. 7 ), where Christ says that we will do everything that he has done, that the only difference is that he has done it first in time, but that time is not real.
This pair of metaphysical teachings, one concerning Islam and the other Christianity strongly suggests the existence of an equivalence of eternal souls before time, that is supported by the sacred teachings of both spiritual traditions. However, the forms of these religions (and all others) are obviously different within the field of space and time. Christians and Muslims have differing concepts about God. However, God is not a concept; no concept, however cherished, can ever contain God.
So maybe it's time, that we all lay down our swords and learn to live the true religion of God --- the religion of Love.