An excerpt from C.S. Lewis, Mere Christianity (Macmillan, 1952), Book 2, Chapter 2, "The Invasion"
Atheism is too simple. And I will tell you another view that is also too simple. It is the view I call Christianity-and-water, the view which simply says there is a good God in Heaven and everything is all right -- leaving out all the difficult and terrible doctrines about sin and hell and the devil, and the redemption. Both these are boys ' philosophies.
It is no good asking for a simple religion. After all, real things are not simple. They look simple, but they are not. The table I am sitting at looks simple: but ask a scientist to tell you what it is really made of--all about the atoms and how the light waves rebound from them and hit my eye and what they do to the optic nerve and what it does to my brain--and, of course, you find that what we call 'seeing a table' lands you in mysteries and complications which you can hardly get to the end of.
A child saying a child's prayer looks simple. And if you are content to stop there, well and good. But if you are not and the modern world usually is not -- if you want to go on and ask what is really happening -- then you must be prepared for something difficult. If we ask for something more than simplicity, it is silly then to complain that the something more is not simple.
Very often, however, this silly procedure is adopted by people who are not silly, but who, consciously or unconsciously, want to destroy Christianity. Such people put up a version of Christianity suitable for a child of six and make that the object of their attack. When you try to explain the Christian doctrine as it is really held by an instructed adult, they then complain that you are making their heads turn round and that it is all too complicated and that if there really were a God they are sure He would have made 'religion' simple, because simplicity is so beautiful, etc. You must be on your guard against these people for they will change their ground every minute and only waste your time. Notice, too, their idea of God 'making religion simple'; as if 'religion' were something God invented, and not His statement to us of certain quite unalterable facts about His own nature.
Besides being complicated, reality, in my experience, is usually odd. It is not neat, not obvious, not what you expect....