One of the books I read while getting my BA in Philosophy at UCLA. The starting point for Idealism in the Western tradition and essential reading for anyone with any interest in Western Philosophy.

As with all philosophy, it is full of sytange and intrique ideas that you really can't prove or disprove. The way I think of the argument is that reality is like a video game or dream. We all "know" that the an object such as a table doesn't really "exist" in a video game. Its only a perception. We we turn off the video game or wake up from a dream, the table is no longer percieved, so it no longer "exists" in external reality. So in reality, how does a table continue to exist when we leave the room(no longer perceive it)? You can't really prove it does ever exist when your not percieving it. Berkeley thinks that it continues to exist as an idea in the mind of God. This God is all-knowing and everywhere at all times. He maintains the constancy of reality. In my opinion, this is a very strong theistic argument.