You're not supposed to understand 2001 like that, it has a different meaning for each and every one of us. That's the whole beauty of the movie, it's like listening to a symphonie and someone saying "Oh, what the composer meant by these notes is that he has lost a loved one and his coutry went to war and the winter was very cold that year and...", no, in fact, we get our own feelings about it, and understand it in different ways. Some songs that make you depressed can make other people happy. In that same way, you cannot "explain" 2001, you can try to verbalize what you understood by it.