The Church is not something dead: it is the body of Christ endowed with supernatural life. As Christ, the Head and Exemplar, is not wholly in His visible human nature . . . nor wholly in the invisible divine nature . . . but is one, from and in both natures, visible and invisible; so the mystical body of Christ is the true Church, only because its visible parts draw life and power from the supernatural gifts and other things whence spring their very nature and essence.
-from On the Unity of the Church (1896)