Objection 1. It would seem that the fire in question will consume the other elements. For a gloss of Bede on 2 Peter 3:12 says: "This exceeding great fire will engulf the four elements whereof the world consists: yet it will not so engulf all things that they will cease to be, but it will consume two of them entirely, and will restore two of them to a better fashion." Therefore it would seem that at least two of the elements are to be entirely destroyed by that fire.
Objection 2. Further, it is written (Apocalypse 21:1): "The first heaven and the first earth have passed away and the sea is no more." Now the heaven here denotes the air, as Augustine states (De Civ. Dei xx, 18); and the sea denotes the gathering together of the waters. Therefore it would seem that these three elements will be wholly destroyed.
Objection 3. Further, fire does not cleanse except in so far as other things are made to be its matter. If, then, fire cleanses the other elements, they must needs become its matter. Therefore they must pass into its nature, and consequently be voided of their own nature.
Objection 4. Further, the form of fire is the most noble of the forms to which elemental matter can attain. Now all things will be brought to the most noble state by this cleansing. Therefore the other elements will be wholly transformed into fire.
On the contrary, A gloss on 1 Corinthians 7:31, "The fashion of this world passeth away," says: "The beauty, not the substance, passeth." But the very substance of the elements belongs to the perfection of the world. Therefore the elements will not be consumed as to their substance.
Further, this final cleansing that will be effected by fire will correspond to the first cleansing which was effected by water. Now the latter did not corrupt the substance of the elements. Therefore neither will the former which will be the work of fire.
I answer that, There are many opinions on this question. For some say that all the elements will remain as to their matter, while all will be changed as regards their imperfection; but that two of them will retain their respective substantial form, namely air and earth, while two of them, namely fire and water, will not retain their substantial form but will be changed to the form of heaven. In this way three elements, namely air, fire, and water, will be called "heaven"; although air will retain the same substantial form as it has now, since even now it is called "heaven." Wherefore (Apocalypse 21:1) only heaven and earth are mentioned: "I saw," says he, "a new heaven and a new earth." But this opinion is altogether absurd: for it is opposed both to philosophy--which holds it impossible for the lower bodies to be in potentiality to the form of heaven, since they have neither a common matter, nor mutual contrariety--and to theology, since according to this opinion the perfection of the universe with the integrity of its parts will not be assured on account of two of the elements being destroyed.
Consequently "heaven" is taken to denote the fifth body, while all the elements are designated by "earth," as expressed in Psalm 148:7-8, "Praise the Lord from the earth" and afterwards, "fire, hail, snow, ice," etc.
Hence others say that all the elements will remain as to their substance, but that their active and passive qualities will be taken from them: even as they say too, that in a mixed body the elements retain their substantial form without having their proper qualities, since these are reduced to a mean, and a mean is neither of the extremes. And seemingly the following words of Augustine (De Civ. Dei xx, 16) would seem in agreement with this: "In this conflagration of the world the qualities of the corruptible elements that were befitting our corruptible bodies will entirely perish by fire: and the substance itself will have those qualities that become an immortal body."
However, this does not seem probable, for since the proper qualities of the elements are the effects of their substantial form, it seems impossible, as long as the substantial forms remain, for the aforesaid qualities to be changed, except for a time by some violent action: thus in hot water we see that by virtue of its species it returns to the cold temperature which it had lost by the action of fire, provided the species of water remain. Moreover, these same elemental qualities belong to the second perfection of the elements, as being their proper passions: nor is it probable that in this final consummation the elements will lose anything of their natural perfection. Wherefore it would seem that the reply to this question should be that the elements will remain as to their substance and proper qualities, but that they will be cleansed both from the stain which they contracted from the sins of men, and from the impurity resulting in them through their mutual action and passion: because when once the movement of the first movable body ceases, mutual action and passion will be impossible in the lower elements: and this is what Augustine calls the "qualities of corruptible elements," namely their unnatural dispositions by reason of which they come near to corruption.
Reply to Objection 1. That fire is said to engulf the four elements in so far as in some way it will cleanse them. But when it is said further that "it will consume two entirely," this does not mean that two of the elements are to be destroyed as to their substance, but that two will be more changed from the property which they have now. Some say that these two are fire and water which excel the others in their active qualities, namely heat and cold, which are the chief principles of corruption in other bodies; and since then there will be no action of fire and water which surpass the others in activity, they would seem especially to be changed from the virtue which they have now. Others, however, say that these two are air and water, on account of the various movements of these two elements, which movements they derive from the movement of the heavenly bodies. And since these movements will cease (such as the ebb and flow of the sea, and the disturbances of winds and so forth), therefore these elements especially will be changed from the property which they have now.
Reply to Objection 2. As Augustine says (De Civ. Dei xx, 16), when it is stated: "And the sea is no more," by the sea we may understand the present world of which he had said previously (De Civ. Dei xx, 13): "The sea gave up the dead that were in it." If, however, the sea be taken literally we must reply that by the sea two things are to be understood, namely the substance of the waters, and their disposition, as containing salt and as to the movement of the waves. The sea will remain, not as to this second, but as to the first.
Reply to Objection 3. This fire will not act save as the instrument of God's providence and power; wherefore it will not act on the other elements so as to consume them but only so as to cleanse them. Nor is it necessary for that which becomes the matter of fire, to be voided of its proper species entirely, as instanced by incandescent iron, which by virtue of its species that remains returns to its proper and former state as soon as it is taken from the furnace. It will be the same with the elements after they are cleansed by fire.
Reply to Objection 4. In the elemental parts we must consider not only what is befitting a part considered in itself, but also what is befitting it in its relation to the whole. I say, then, that although water would be more noble if it had the form of fire, as likewise would earth and air, yet the universe would be more imperfect, if all elemental matter were to assume the form of fire.
Source: Summa Theologica (New Advent)