There are two things. The deeper I think about them, the longer they last, and the more they arouse admiration and awe in my heart. One is the vast and splendid starry sky above us, and the other is the lofty moral law in our hearts. They proved to me that God is on my head and in my heart.

This is one of the most magnificent maxims in the history of human thought. It is engraved on Kant's tombstone and comes from the last chapter of Kant's Critique of Practical Reason.