What do we mean by spiritual development? Surely, the broadening and deepening of the mind till it regards the world in its true perspective, and the strengthening of the character so that the will is a tempered and unerring weapon in the charge of a man's soul. And this end is to be achieved only by the exercise of the mind upon the largest possible manifold of experience, and by the conflict of character with the alien forces of the world.

Ch. XII, pp. 336–7 - A Lodge in the Wilderness (1906)