From The Everlasting Man by G. K. Chesterton:
It means that somehow or other a new thing had appeared in the cavernous night of nature, a mind that is like a mirror. It is like a mirror because it is truly a thing of reflection. It is like a mirror because in it alone all the other shapes can be seen like shining shadows in a vision. Above all, it is like a mirror because it is the only thing of its kind. Other things may resemble it or resemble each other in various ways; other things may excel it or excel each other in various ways; just as in the furniture of a room a table may be round like a mirror or a cupboard may be larger than a mirror. But the mirror is the only thing that can contain them all. Man is the microcosm; man is the measure of all things; man is the image of God.
…Alone among the animals, he is shaken with the beautiful madness called laughter; as if he had caught sight of some secret in the very shape of the universe hidden from the universe itself.