Well, by "spirit", I mean that they were written in accordance with certain moral principles which are intended to create civility and order within their culture, which is governed by their worldview. Christians and Muslims do not, in my opinion, worship the same God. Neither do Christians and Jews. In my opinion, the difference between the Jewish God (the god of the old testament) and the Christian God (the god of the New testament) are two totally different gods. Obviously, the argument can be made that it was not God who changed, but his convenant (relationship) with Man, but that distinction, to me, is a small one; and not one of great importance. Why should a divine God change? However, I would say they are two different versions of the same God, connected only by a shared mythology (or scripture). However, Islam is set itself up as antagonistic toward Christians and Jews; how you could be so antagonistic toward followers of the same god, I do not know.