When we look upon anything, though it is present to us, it is not itself united to our eyes, but only sends out to them a certain representation or picture of itself, which is called its sensible species, by means of which we see. So also when we contemplate or understand anything, that which we understand is not united to our understanding otherwise than by another representation and most delicate and spiritual image, which is called intelligible species. But further, these species, by how many windings and changes do they get to the understanding! They arrive at the exterior senses, thence pass to the interior, then to the imagination, then to the active understanding, and come at last to the passive understanding, to the end that passing through so many strainers and under so many files they may be purified, subtilised and perfected, and of sensible become intelligible.

Thus, Theotimus, we see and understand all that we see and understand in this mortal life, yea even things of faith; for, as the mirror contains not the thing we see in it but only the representation and species of it (which representation, stayed by the mirror, produces another in the beholding eye), so the word of faith does not contain the things which it announces, but only represents them, and this representation of divine things which is in the word of faith produces another representation of them, which our understanding, helped by God's grace, accepts and receives as a representation of holy truth, and our will takes delight in it, and embraces it, as an honourable, profitable, lovely and excellent truth. Thus the truths signified in God's word are by it represented to the understanding as things expressed in the mirror are by the mirror represented to the eye: whence the great Apostle said that to believe is to see as in a glass.