Christmas is proof of many things. It proves we love our children – we’ll make great sacrifices to buy them gifts. It proves there’s still nostalgia in our souls – we just love the thought of a white Christmas.

It proves we can still sing – we can manage Once in Royal David’s City even when half cut. It proves we love special meals – that blow out on Christmas Day has been planned for weeks. It proves the Queen still exists – there she is again at 3 o’clock.
But does it prove that God exists?

For me to try and prove that God exists would be like Harry Potter trying to prove that J.K.Rowling exists. How could he? He’s in a story written by J.K.Rowling; he’s not in the same framework of existence as the author of the story herself. If Harry was to believe in her, J.K.Rowling would have to have given Harry some information about herself in the story she was writing.

So if we’re to believe in the divine Author, he would have to give us some information about himself in the story he’s writing about Life. But Christmas says he’d done more than that – he’s written himself into the story in the lead role. He’s not just given us a website to look up; he’s stepped into the narrative itself as the main character.

And this character is the attractive, compelling, gracious figure who has fascinated the world for two thousand and more years. He’s the plot, the sub-plot, the chapter heading and the footnotes of Christianity.

At Christmas of course, the story is only just beginning. But the Author has arrived; everything is different; the plot has to be radically re-written.
None of us can prove that God exists, but Christmas says that God proves himself by coming among us in person, a person who loves us to bits.
Now that really does call for a celebration!

The Rt Revd John Pritchard is Bishop of Oxford.