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.
But in heaven, Theotimus, -- Ah! my God, what a favour! -- The Divinity will unite itself to our understanding without the mediation of any species or representation at all, but it will itself apply and join itself to our understanding, making itself in such sort present unto it, that that inward presence shall be instead of a representation or species. O God! what sweetness shall it be for man's understanding to be united for ever to its sovereign object, receiving not its representation but its presence, not the picture or species, but the very essence of its divine truth and majesty. We shall be there as most happy children of the divinity, and shall have the honour to be fed with the divine substance itself, taken into our soul by the mouth of our understanding, and what surpasses all sweetness is, that as mothers are not contented with feeding their babes with their milk, which is their own substance, if they do not also put the breast into their mouth, that these may receive their substance, not in a spoon or other instrument, but even in, and by this same substance (so that this maternal substance serves as well for food, as for a conduit to convey it to the dear little suckling); -- so God our Father is not contented to make us receive his proper substance in our understanding, that is, to make us see his divinity, but by an abyss of his sweetness, wills himself to apply his substance to our soul, to the end that we may no longer understand it by species or representation but in itself and by itself; so that his fatherly and eternal substance is both species and object to our understanding. Then these divine promises shall be fulfilled in an excellent manner: I will lead her into the wilderness, and I will speak to her heart, and give her suck. Rejoice with Jerusalem and be glad with her. That you may suck and be filled with the breasts of her consolations, that you may milk out, and flow with delights from the abundance of her glory: you shall be carried at the breasts, and upon the knees they shall caress you.
Infinite bliss, Theotimus, and one which has not been promised only, but of which we have a pledge in the Blessed Sacrament, that perpetual feast of Divine Grace. For in it we receive the blood of Our Saviour in his flesh, and his flesh in his blood; his blood being applied unto us by means of his flesh, his substance by his substance to our very corporal mouth; that we may know that so he will apply unto us his divine essence in the eternal feast of his glory. True it is, this favour is done unto us here really but covertly, under Sacramental species and appearances, whereas in heaven, the Divinity will give himself openly, and we shall see him face to face as he is.