Since it is impossible for a natural desire to be incapable of fulfilment, and since it would be so, if it were not possible to reach an understanding of divine substance such as all minds naturally desire, we must say that it is possible for the substance of God to be seen intellectually, both by separate intellectual substances and by our souls.
 It is already sufficiently apparent from what we have said what should be the mode of this vision. For we showed above that the divine substance cannot be seen intellectually by means of any created species. Consequently, if the divine essence is seen, it must be done as His intellect sees the divine essence itself through itself, and in such a vision the divine essence must be both what is seen and that whereby it is seen.
 Now, since the created intellect cannot understand any substance unless it becomes actual by means of some species, which is the likeness of the thing understood, informing it, a person might consider it impossible for a created intellect to be able to see, by means of the divine essence serving as a sort of intelligible species, the very substance of God. For the divine essence is a certain being subsisting through itself, and we showed in Book One  that God cannot be a form for any other being.
 In order to understand the truth of this matter, we must consider that self-subsistent substance is either a form only, or a composite of matter and form. And a thing composed of matter and form cannot be the form of another being, because the form in it is already limited to this matter in such a way that it could not be the form of another thing. But a being which subsists in such a way that it is a form only can be the form of another, provided its being is such that it could be participated by that other thing, as we showed concerning the human soul, in Book Two . However, if its being could not be participated by another, it could not be the form of any other thing, for then it would be determined within itself by its own being, just as material things are by their own matter.
Now, this should be observed as obtaining in the same way in the order of intelligible being as it does in substantial or physical being. For, since the perfection of the intellect is what is true, in the order of intelligible objects, that object which is a purely formal intelligible will be truth itself. And this characteristic applies only to God, for, since the true is consequent on being, that alone is its own truth which is its own being. But this is proper to God only, as we showed in Book Two . So, other intelligible subsistents do not exist as pure forms in the order of intelligible beings, but as possessors of a form in some subject. In fact, each of them is a true thing but not truth, just as each is a being but not the very act of being.
So, it is manifest that the divine essence may be related to the created intellect as an intelligible species by which it understands, but this does not apply to the essence of any other separate substance. Yet, it cannot be the form of another thing in its natural being, for the result of this would be that, once joined to another thing, it would make up one nature. This could not be, since the divine essence is in itself perfect in its own nature. But an intelligible species,(united with an intellect, does not make up a nature; rather, it perfects the intellect for the act of understanding, and this is not incompatible with the perfection of the divine essence.
 This immediate vision of God is promised us in Scripture: “We see now through a glass in a dark manner; but then face to face” (1 Cor. 13:12). It is wrong to understand this in a corporeal way, picturing in our imagination a bodily face of the Divinity, since we have shown that God is incorporeal. Nor is it even possible for us to see God with our bodily face, for the power of corporeal vision, which is associated with our face, can only apply to corporeal things. Thus, then, shall we see God face to face, in the sense that we shall see Him without a medium, as is true when we see a man face to face.
 In this vision, of course, we become most like unto God, and we are partakers in His happiness. For God Himself understands His own substance through His own essence; and this is His felicity. Hence it is said: “When He shall appear, we shall be like to Him, because we shall see Him as He is” (1 John 3:2). And the Lord says “I dispose to you, as My Father has disposed to me... my table, that you may eat and drink at my table, in my kingdom” (Luke 22:29-30). Of course, this can be understood not in reference to corporeal food or drink, but to Him who is received at the table of Wisdom, of whom Wisdom speaks: “Eat My bread and drink the wine which I have mingled for you” (Proverbs 9:5). And so, may they who enjoy the same felicity whereby God is happy eat and drink at God’s table, seeing Him in the way that lie sees Himself.
Next - CONTRA GENTILES - BOOK THREE: PROVIDENCE -Chapter 52 THAT NO CREATED SUBSTANCE CAN, BY ITS OWN NATURAL POWER, ATTAIN THE VISION OF GOD IN HIS ESSENCE