There seem to be three big categories that divide humanity by what they believe or don't believe about God. Professor Lewis gets a bit deep here and so this is one of the places where I have tried to simplify and not being a theologian or philosopher, hopefully I did not go wrong in trying to be simple.
My chart is the ultimate in simplification of what are concepts that have fine lines and gather great debates ... just go to Google and you can find yourself reading for hours and understanding less the more you read. But for Professor Lewis these distinctions are important aspects of how he arrives on Christianity's doorstep as the himself sorts these views.
Lewis sees Pantheists as those that call one thing both good and bad. "We call a cancer bade, they would say, because it kills a man; but you might just as well call a successful surgeon bad because he kills a cancer. It all depends upon a point of view. It was professed by the great Prussian philosppher Hegel and describes many of the beliefs of Far Eastern religions.
Lewis sees Christians as those that believe God made the universe. "Space, time, heat and cold, and allthe colors and tastes, and all the animals and vegetables are all things that God made up out of His head as a man makes up a story. He is all good, and worthy of our worship.
Lewis sees Atheists as those who have to reject what all other people on earth believe. He started out as an atheist and long defended his views against his Christian friends, until he actually tried to understand his objections and that is when he became a Christian.