Can a Christian have a demon? Consider the following. The world is a very large place in our eyes, but in God’s eyes (He is the Creator of the Universe) it is a very small place. Yet in this “small place,” (the world) evil and good co-exist – they live in the same place. Of course, it you want to analyze it a bit more, you might say, “Well, they don’t really co-exist, they live separately, in different regions of the word. In one house there is good, while in the other house there is evil.”
We are created human beings, and we often don’t see “in the spiritual,” but “in the natural.” We must, however, begin to see “in the spiritual” if we are going to understand spiritual things. Again, to God, the world is a very small place. I wouldn’t be surprised that if, to God, the size of world was like a fraction of the size of a grain of sand by our standard of measure — it is that small (think of the billions and billions of galaxies, and billions and billions of stars in each galaxy — mind boggling, to say the least). If the size of the world is then “that small” to God (and I think we can assume, somehow, that it is), how could a demon and the Holy Spirit possible exist in the “same place?” The answer, of course, is that it is not the “same place,” but different places.
Now no-one has really been able to understand how light really works. At times, it is said to behave like waves, while at other times it is said to behave like particles. So, too, I think we can “excuse ourselves” in a sense, for not fully understanding how the human heart works — it is a complicated thing. Yet I think we can say, that one good analogy is that is like a building with many separate “compartments.” That a demon could occupy one of those compartments, while the Holy Spirit occupies another one of those compartments I do not think should be a very complicated thing to accept.
Again, let us not look with our physical eyes. To us, that is a very close distance apart. But we are not dealing with physical distances here. We are dealing with spiritual realities. And we know what Jesus said about the devil: “he has nothing in Me.” (John 14:30). The devil did not have anything “in” Jesus (could not get a grip on his life, or His heart, which really is the issue we are dealing with here) because Jesus was without sin (Hebrew 4:15). The issue, then, is not one of distance (how big the heart is, how big a demon is that might occupy that heart, etc.) but one of sin. Repeatedly, the Bible tells us that sin opens the door for the devil. Why then should we be amazed if the devil has a hold in our life?