The answer that I see most often in spiritual writings is that God is on a mission of self discovery. He is trying to understand himself and his capabilities by creating various lesser beings and observing them. At first, this answer seems to make a lot of sense, but when you think about it a bit more, you might notice one serious flaw in this theory: it implies that there are things that God does not know and therefore is trying to learn. That, of course, cannot be true.

    Another simpler theory works better for me. God is simply thinking. Because He is God, whatever he things, He creates merely by thinking about it. Since God things about the things He already knows, he creates accordingly. He does not create something He knows nothing about, then tries to figure out what it is and what it does, that doesn't make sense.

    Just think of how humans create. A person who is a computer expert doesn't suddenly invent a new rocket fuel because fuels are something he knows nothing about. If a computer expert invents something, it will be related to the field he knows. The same with other experts. And, while it is true that people invent new things by taking the knowledge they already have, and then doing experiments to learn more, to assume that God would do the same type of experimentation is to bring him down to our level which is simply not true.

    God already knows everything that exists now, in the past, and in the future. And, if there was something that He didn't know, He could never learn it, because He is the source of all knowledge.