The Christian Ideal

Where did Chesterton say, “The Christian ideal has not been tried and found wanting. It has been found difficult; and left untried.”?

The line comes from Chesterton’s must-read book, What’s Wrong with the World, which we never get tired of saying, seems like it was written ten minutes ago, rather than 88 years ago. The line comes from Part I, Chapter 5, “The Unfinished Temple.”