This quote is from the book The Lion, the Witch, and the Wardrobe by C.S. Lewis. It means that the speaker will continue to live according to the values of Narnia even if its existence can’t be proven. Aslan is a character in this book that symbolizes goodness and kindness. So, the quote suggests that the speaker will continue to practice these values even if Aslan is not real because these are the values of Narnia.