(CG 3/52). That no Created Substance can of its natural power arrive to se... (Book 3. God, the End of Creatures) (Summa Contra Gentiles) (Aquinas, Thomas, St.)

IT is impossible for that which is the proper form of one thing to become the form of another thing, unless that latter thing comes to partake of some likeness to the former. But the divine essence is the proper intelligible form of the divine intelligence, and is proportioned to it: for in God these three are one, that which understands, that whereby it understands, and that which is understood. It is impossible therefore for the very essence of God to become an intelligible form to any created intellect otherwise than by the said intellect coming to be partaker in some likeness to God.

3. If two things, not previously united, come afterwards to be united, this must be either by a change in both or by a change in one of them. If therefore any created intellect begins anew to see the essence of God, the divine essence must be conjoined anew with that intellect by way of intelligible presentation. But it is impossible for the divine essence to change; and therefore such union must begin by some change in the created intellect, that is to say, by its making some new acquisition.

But because we arrive at the knowledge of things intelligible through things sensible, we also transfer the names of sensible cognition to intelligible cognition, and particularly the properties of sight, which among senses is the nobler and more spiritual and more akin to intellect: hence intellectual knowledge itself is called sight, or vision. And because bodily vision is not accomplished except through light, the means whereby intellectual vision is fulfilled borrow the name of light. That disposition therefore whereby a created intelligence is raised to the intellectual vision of the divine substance is called the 'light of glory.'

This is the light of which it is said: In your light we shall see light (Ps. xxxv, 10), to wit, of the divine substance; and, The city needeth not sun nor moon, for the brightness of God illuminateth it (Apoc. xxi, 23); and, No more shall there be sun to shine on you by day, nor brightness of moon to enlighten you, but the Lord shall be to you an everlasting light, and your God shall be your glory Isaias lx, 19). And because in God being and understanding are the same and He is to all the cause of understanding, He is on that account called 'light': He was the true light, that enlighteneth every man coming into this world John i, 8): God is light (1 John i, 5): Clad in light as in a garment (Ps. ciii, 2). And therefore also as well God as the angels in Holy Scripture are described in figures of fire, because of the brightness of fire.

3.52 : That no Created Substance can of its Natural Power arrive to see God as He essentially is
3.54 : Arguments against the aforesaid Statements and their Solutions