Objection 1. It would seem that the blessed do not rejoice in the punishment of the wicked. For rejoicing in another's evil pertains to hatred. But there will be no hatred in the blessed. Therefore they will not rejoice in the unhappiness of the damned.
Objection 2. Further, the blessed in heaven will be in the highest degree conformed to God. Now God does not rejoice in our afflictions. Therefore neither will the blessed rejoice in the afflictions of the damned.
Objection 3. Further, that which is blameworthy in a wayfarer has no place whatever in a comprehensor. Now it is most reprehensible in a wayfarer to take pleasure in the pains of others, and most praiseworthy to grieve for them. Therefore the blessed nowise rejoice in the punishment of the damned.
On the contrary, It is written (Psalm 57:11): "The just shall rejoice when he shall see the revenge."
Further, it is written (Isaiah 56:24): "They shall satiate [Douay: 'They shall be a loathsome sight to all flesh.'] the sight of all flesh." Now satiety denotes refreshment of the mind. Therefore the blessed will rejoice in the punishment of the wicked.
I answer that, A thing may be a matter of rejoicing in two ways. First directly, when one rejoices in a thing as such: and thus the saints will not rejoice in the punishment of the wicked. Secondly, indirectly, by reason namely of something annexed to it: and in this way the saints will rejoice in the punishment of the wicked, by considering therein the order of Divine justice and their own deliverance, which will fill them with joy. And thus the Divine justice and their own deliverance will be the direct cause of the joy of the blessed: while the punishment of the damned will cause it indirectly.
Reply to Objection 1. To rejoice in another's evil as such belongs to hatred, but not to rejoice in another's evil by reason of something annexed to it. Thus a person sometimes rejoices in his own evil as when we rejoice in our own afflictions, as helping us to merit life: "My brethren, count it all joy when you shall fall into divers temptations" (James 1:2).
Reply to Objection 2. Although God rejoices not in punishments as such, He rejoices in them as being ordered by His justice.
Reply to Objection 3. It is not praiseworthy in a wayfarer to rejoice in another's afflictions as such: yet it is praiseworthy if he rejoice in them as having something annexed. However it is not the same with a wayfarer as with a comprehensor, because in a wayfarer the passions often forestall the judgment of reason, and yet sometimes such passions are praiseworthy, as indicating the good disposition of the mind, as in the case of shame pity and repentance for evil: whereas in a comprehensor there can be no passion but such as follows the judgment of reason.
Source: Summa Theologica (New Advent)