So humble is his mercy that since we cannot raise our understandings to the comprehension of divine mysteries, he will bring down, and submit those mysteries to the apprehension of our senses. Hereafter our bodies shall be over-clothed with a spiritual glory by a real union unto Christ in his kingdom; mean time that spiritual glory which we groan after, is here over-clothed with weak and visible elements, by a Sacramental union at his Table.
Then shall sense be exalted and made a fit subject of glory, here (in the Sacrament) is glory humbled, and made a fit object of sense. Then shall we see as we are seen, face to face; here we see but as in glass darkly; in the glass of the creature, in the glass of the Word, in the glass of the Sacraments. Surely these are in themselves clear and bright glasses, yet we see even in them but darkly, in regard of that vapor and steam which exhales from our corrupt nature, when we use them: and even on these do our souls look through other dark glasses, the windows of sense. At best they are but glasses, whose properties are to present nothing but the pattern, the shadow, the type of those things which are in their substance quite behind us, and therefore out of sight.
So then in general, the nature of a Sacrament is to be the representative of a substance, the sign of a covenant, the seal of a purchase, the figure of a body, the witness of our faith, the earnest of our hope, the presence of things distant, the sight of things absent, the taste of things inconceivable, and the knowledge of things, that are past knowledge.