Christianity satisfies suddenly and perfectly man's ancestral instinct for being the right way up; satisfies it supremely in this, that by its creed Joy becomes something gigantic, and Sadness something special and small.
The point is not that this world is too sad to love or too glad not to love; the point is that when you do love a thing, its gladness is a reason for loving it, and its sadness a reason for loving it more.