Today I was just looking at some old C.S Lewis quotes and one really caught my eye.
I believe in Christianity as I believe that the sun has risen: not only because I see it, but because by it I see everything else. 
C. S. Lewis 
Read more at http://www.brainyquote.com/quotes/authors/c/c_s_lewis.html#lUZHGh5xmh9glrt8.99

It not only reminds me that he is as real as the most simple, believable things as the sun, but also this is a great metaphor to indicate that we know christianity is right because once you know the truth, everything else answers itself and it lights up the answers, just as the sunrise lights up the world showing its real and alive.