Objection 1. It would seem that after the resurrection the saints will see God with the eyes of the body. Because the glorified eye has greater power than one that is not glorified. Now the blessed Job saw God with his eyes (Job 42:5): "With the hearing of the ear, I have heard Thee, but now my eye seeth Thee." Much more therefore will the glorified eye be able to see God in His essence.
Objection 2. Further, it is written (Job 19:26): "In my flesh I shall see God my Saviour [Vulgate: 'my God']." Therefore in heaven God will be seen with the eyes of the body.
Objection 3. Further. Augustine, speaking of the sight of the glorified eyes, expresses himself as follows (De Civ. Dei xxii): "A greater power will be in those eyes, not to see more keenly, as certain serpents or eagles are reported to see (for whatever acuteness of vision is possessed by these animals they can see only corporeal things), but to see even incorporeal things." Now any power that is capable of knowing incorporeal things can be upraised to see God. Therefore the glorified eyes will be able to see God.
Objection 4. Further, the disparity of corporeal to incorporeal things is the same as of incorporeal to corporeal. Now the incorporeal eye can see corporeal things. Therefore the corporeal eye can see the incorporeal: and consequently the same conclusion follows.
Objection 5. Further, Gregory, commenting on Job 4:16, "There stood one whose countenance I knew not," says (Moral. v): "Man who, had he been willing to obey the command, would have been spiritual in the flesh, became, by sinning, carnal even in mind." Now through becoming carnal in mind, "he thinks only of those things which he draws to his soul by the images of bodies" (Moral. v). Therefore when he will be spiritual in the flesh (which is promised to the saints after the resurrection), he will be able even in the flesh to see spiritual things. Therefore the same conclusion follows.
Objection 6. Further, man can be beatified by God alone. Now he will be beatified not only in soul but also in body. Therefore God will be visible not only to his intellect but also to his flesh.
Objection 7. Further, even as God is present to the intellect by His essence, so will He be to the senses, because He will be "all in all" (1 Corinthians 15:28). Now He will be seen by the intellect through the union of His essence therewith. Therefore He will also be visible to the sense.
On the contrary, Ambrose, commenting on Luke 1:2, "There appeared to him an angel," says: "God is not sought with the eyes of the body, nor surveyed by the sight, nor clasped by the touch." Therefore God will by no means be visible to the bodily sense.
Further, Jerome, commenting on Isaiah 6:1, "I saw the Lord sitting," says: "The Godhead not only of the Father, but also of the Son and of the Holy Ghost is visible, not to carnal eyes, but only to the eyes of the mind, of which it is said: Blessed are the pure in heart."
Further, Jerome says again (as quoted by Augustine, Ep. cxlvii): "An incorporeal thing is invisible to a corporeal eye." But God is supremely incorporeal. Therefore, etc.
Further, Augustine says (De Videndo Deo, Ep. cxlvii): "No man hath seen God as He is at any time, neither in this life, nor in the angelic life, in the same way as these visible things which are seen with the corporeal sight." Now the angelic life is the life of the blessed, wherein they will live after the resurrection. Therefore, etc.
Further, according to Augustine (De Trin. xiv.), "man is said to be made to God's image inasmuch as he is able to see God." But man is in God's image as regards his mind, and not as regards his flesh. Therefore he will see God with his mind and not with his flesh.
I answer that, A thing is perceptible to the senses of the body in two ways, directly and indirectly. A thing is perceptible directly if it can act directly on the bodily senses. And a thing can act directly either on sense as such or on a particular sense as such. That which acts directly in this second way on a sense is called a proper sensible, for instance color in relation to the sight, and sound in relation to the hearing. But as sense as such makes use of a bodily organ, nothing can be received therein except corporeally, since whatever is received into a thing is therein after the mode of the recipient. Hence all sensibles act on the sense as such, according to their magnitude: and consequently magnitude and all its consequences, such as movement, rest, number, and the like, are called common sensibles, and yet they are direct objects of sense.
An indirect object of sense is that which does not act on the sense, neither as sense nor as a particular sense, but is annexed to those things that act on sense directly: for instance Socrates; the son of Diares; a friend and the like which are the direct object of the intellect's knowledge in the universal, and in the particular are the object of the cogitative power in man, and of the estimative power in other animals. The external sense is said to perceive things of this kind, although indirectly, when the apprehensive power (whose province it is to know directly this thing known), from that which is sensed directly, apprehends them at once and without any doubt or discourse (thus we see that a person is alive from the fact that he speaks): otherwise the sense is not said to perceive it even indirectly.
I say then that God can nowise be seen with the eyes of the body, or perceived by any of the senses, as that which is seen directly, neither here, nor in heaven: for if that which belongs to sense as such be removed from sense, there will be no sense, and in like manner if that which belongs to sight as sight be removed therefrom, there will be no sight. Accordingly seeing that sense as sense perceives magnitude, and sight as such a sense perceives color, it is impossible for the sight to perceive that which is neither color nor magnitude, unless we call it a sense equivocally. Since then sight and sense will be specifically the same in the glorified body, as in a non-glorified body, it will be impossible for it to see the Divine essence as an object of direct vision; yet it will see it as an object of indirect vision, because on the one hand the bodily sight will see so great a glory of God in bodies, especially in the glorified bodies and most of all in the body of Christ, and, on the other hand, the intellect will see God so clearly, that God will be perceived in things seen with the eye of the body, even as life is perceived in speech. For although our intellect will not then see God from seeing His creatures, yet it will see God in His creatures seen corporeally. This manner of seeing God corporeally is indicated by Augustine (De Civ. Dei xxii), as is clear if we take note of his words, for he says: "It is very credible that we shall so see the mundane bodies of the new heaven and the new earth, as to see most clearly God everywhere present, governing all corporeal things, not as we now see the invisible things of God as understood by those that are made, but as when we see men... we do not believe but see that they live."
Reply to Objection 1. This saying of Job refers to the spiritual eye, of which the Apostle says (Ephesians 1:18): "The eyes of our [Vulgate: 'your'] heart enlightened."
Reply to Objection 2. The passage quoted does not mean that we are to see God with the eyes of the flesh, but that, in the flesh, we shall see God.
Reply to Objection 3. In these words Augustine speaks as one inquiring and conditionally. This appears from what he had said before: "Therefore they will have an altogether different power, if they shall see that incorporeal nature": and then he goes on to say: "Accordingly a greater power," etc., and afterwards he explains himself.
Reply to Objection 4. All knowledge results from some kind of abstraction from matter. Wherefore the more a corporeal form is abstracted from matter, the more is it a principle of knowledge. Hence it is that a form existing in matter is in no way a principle of knowledge, while a form existing in the senses is somewhat a principle of knowledge, in so far as it is abstracted from matter, and a form existing in the intellect is still better a principle of knowledge. Therefore the spiritual eye, whence the obstacle to knowledge is removed, can see a corporeal object: but it does not follow that the corporeal eye, in which the cognitive power is deficient as participating in matter, be able to know perfectly incorporeal objects of knowledge.
Reply to Objection 5. Although the mind that has become carnal cannot think but of things received from the senses, it thinks of them immaterially. In like manner whatever the sight apprehends it must always apprehend it corporeally: wherefore it cannot know things which cannot be apprehended corporeally.
Reply to Objection 6. Beatitude is the perfection of man as man. And since man is man not through his body but through his soul, and the body is essential to man, in so far as it is perfected by the soul: it follows that man's beatitude does not consist chiefly otherwise than in an act of the soul, and passes from the soul on to the body by a kind of overflow, as explained above (Question 85, Article 1). Yet our body will have a certain beatitude from seeing God in sensible creatures: and especially in Christ's body.
Reply to Objection 7. The intellect can perceive spiritual things, whereas the eyes of the body cannot: wherefore the intellect will be able to know the Divine essence united to it, but the eyes of the body will not.
Source: Summa Theologica (New Advent)