Objection 1. It would seem that the Godhead can be seen by the wicked without joy. For there can be no doubt that the wicked will know with the greatest certainty that Christ is God. Therefore they will see His Godhead, and yet they will not rejoice in seeing Christ. Therefore it will be possible to see it without joy.
Objection 2. Further, the perverse will of the wicked is not more adverse to Christ's humanity than to His Godhead. Now the fact that they will see the glory of His humanity will conduce to their punishment, as stated above (2, ad 4). Therefore if they were to see His Godhead, there would be much more reason for them to grieve rather than rejoice.
Objection 3. Further, the course of the affections is not a necessary sequel to that which is in the intellect: wherefore Augustine says (In Ps. 118: conc. 8): "The intellect precedes, the affections follow slowly or not at all." Now vision regards the intellect, whereas joy regards the affections. Therefore it will be possible to see the Godhead without joy.
Objection 4. Further, whatever is received into "a thing is received according to the mode of the receiver and not of the received." But whatever is seen is, in a way, received into the seer. Therefore although the Godhead is in itself supremely enjoyable, nevertheless when seen by those who are plunged in grief, it will give no joy but rather displeasure.
Objection 5. Further, as sense is to the sensible object, so is the intellect to the intelligible object. Now in the senses, "to the unhealthy palate bread is painful, to the healthy palate sweet," as Augustine says (Confess. vii), and the same happens with the other senses. Therefore since the damned have the intellect indisposed, it would seem that the vision of the uncreated light will give them pain rather than joy.
On the contrary, It is written (John 17:3): "This is eternal life: That they may know Thee, the... true God." Wherefore it is clear that the essence of bliss consists in seeing God. Now joy is essential to bliss. Therefore the Godhead cannot be seen without joy.
Further, the essence of the Godhead is the essence of truth. Now it is delightful to every one to see the truth, wherefore "all naturally desire to know," as stated at the beginning of the Metaphysics. Therefore it is impossible to see the Godhead without joy.
Further, if a certain vision is not always delightful, it happens sometimes to be painful. But intellective vision is never painful since "the pleasure we take in objects of understanding has no grief opposed to it," according to the Philosopher (Topic. ii). Since then the Godhead cannot be seen save by the intellect, it seems that the Godhead cannot be seen without joy.
I answer that, In every object of appetite or of pleasure two things may be considered, namely the thing which is desired or which gives pleasure, and the aspect of appetibility or pleasurableness in that thing. Now according to Boethius (De Hebdom.) that which is can have something besides what it is, but 'being' itself has no admixture of aught else beside itself. Hence that which is desirable or pleasant can have an admixture of something rendering it undesirable or unpleasant; but the very aspect of pleasurableness has not and cannot have anything mixed with it rendering it unpleasant or undesirable. Now it is possible for things that are pleasurable, by participation of goodness which is the aspect of appetibility or pleasurableness, not to give pleasure when they are apprehended, but it is impossible for that which is good by its essence not to give pleasure when it is apprehended. Therefore since God is essentially His own goodness, it is impossible for the Godhead to be seen without joy.
Reply to Objection 1. The wicked will know most clearly that Christ is God, not through seeing His Godhead, but on account of the most manifest signs of His Godhead.
Reply to Objection 2. No one can hate the Godhead considered in itself, as neither can one hate goodness itself. But God is said to be hated by certain persons in respect of some of the effects of the Godhead, in so far as He does or commands something contrary to their will [Cf. II-II, 34, 1]. Therefore the vision of the Godhead can be painful to no one.
Reply to Objection 3. The saying of Augustine applies when the thing apprehended previously by the intellect is good by participation and not essentially, such as all creatures are; wherefore there may be something in them by reason of which the affections are not moved. In like manner God is known by wayfarers through His effects, and their intellect does not attain to the very essence of His goodness. Hence it is not necessary that the affections follow the intellect, as they would if the intellect saw God's essence which is His goodness.
Reply to Objection 4. Grief denotes not a disposition but a passion. Now every passion is removed if a stronger contrary cause supervene, and does not remove that cause. Accordingly the grief of the damned would be done away if they saw God in His essence.
Reply to Objection 5. The indisposition of an organ removes the natural proportion of the organ to the object that has a natural aptitude to please, wherefore the pleasure is hindered. But the indisposition which is in the damned does not remove the natural proportion whereby they are directed to the Divine goodness, since its image ever remains in them. Hence the comparison fails.
Source: Summa Theologica (New Advent)