You wrote: “My christian religion differs from that of islam yet the best description I ever heard for the existence of God came from a muslim. He said that people could say there was no God, but he didn't believe them. He didn't believe because he said he could feel God inside- inside his heart.
Christians say that there is a place inside of us that only God can fill.”
Many people claim same thing. I have been in many churches and met many Christians and pastors and almost all of them have such claims as: “I have GOD in the heart,” or “God put in my heart…,” and other similar statements. But looking at these people closely I found that they lie, because their process of thought and they deeds reveal completely opposite of that they are saying.
Also some people believe, “from the heart” in Santa, in Korma, and in all sorts of superstitious things, and of course they are all claming that these things are true.
But I know for sure, that if GOD enters a man, it will be immediately, not only noticed by a man himself, but also and other people who will see him, and as such examples in the Bible are many.