Objection 1. It would seem that the time of the resurrection ought not to be delayed till the end of the world, so that all may rise together. For there is more conformity between head and members than between one member and another, as there is more between cause and effect than between one effect and another. Now Christ, Who is our Head, did not delay His resurrection until the end of the world, so as to rise again together with all men. Therefore there is no need for the resurrection of the early saints to be deferred until the end of the world, so that they may rise again together with the others.
Objection 2. Further, the resurrection of the Head is the cause of the resurrection of the members. But the resurrection of certain members that desire nobility from their being closely connected with the Head was not delayed till the end of the world, but followed immediately after Christ's resurrection, as is piously believed concerning the Blessed Virgin and John the Evangelist [Ep. de Assump. B.V., cap. ii, among St. Jerome's works]. Therefore the resurrection of others will be so much nearer Christ's resurrection, according as they have been more conformed to Him by grace and merit.
Objection 3. Further, the state of the New Testament is more perfect, and bears a closer resemblance to Christ, than the state of the Old Testament. Yet some of the fathers of the Old Testament rose again when Christ rose, according to Matthew 27:52: "Many of the bodies of the saints, that had slept, arose." Therefore it would seem that the resurrection of the Old Testament saints should not be delayed till the end of the world, so that all may rise together.
Objection 4. Further, there will be no numbering of years after the end of the world. Yet after the resurrection of the dead, the years are still reckoned until the resurrection of others, as appears from Apocalypse 20:4-5. For it is stated there that "I saw... the souls of them that were beheaded for the testimony of Jesus, and for the word of God," and further on: "And they lived and reigned with Christ a thousand years." And "the rest of the dead lived not till the thousand years were finished." Therefore the resurrection of all is not delayed until the end of the world, that all may rise together.
On the contrary, It is written (Job 14:12): "Man when he is fallen asleep shall not rise again till the heavens be broken, he shall not wake, nor rise out of his sleep," and it is a question of the sleep of death. Therefore the resurrection of men will be delayed until the end of the world when the heavens shall be broken.
Further, it is written (Hebrews 11:39): "All these being approved by the testimony of faith received not the promise," i.e. full beatitude of soul and body, since "God has provided something better for us, lest they should be consummated," i.e. perfected, "without us--in order that," as a gloss observes, "through all rejoicing each one might rejoice the more." But the resurrection will not precede the glorification of bodies, because "He will reform the body of our lowness made like to the body of His glory" (Philippians 3:21), and the children of the resurrection will be "as the angels... in heaven" (Matthew 22:30). Therefore the resurrection will be delayed till the end of the world, when all shall rise together.
I answer that, As Augustine states (De Trin. iii, 4) "Divine providence decreed that the grosser and lower bodies should be ruled in a certain order by the more subtle and powerful bodies": wherefore the entire matter of the lower bodies is subject to variation according to the movement of the heavenly bodies. Hence it would be contrary to the order established in things by Divine providence if the matter of lower bodies were brought to the state of incorruption, so long as there remains movement in the higher bodies. And since, according to the teaching of faith, the resurrection will bring men to immortal life conformably to Christ Who "rising again from the dead dieth now no more" (Romans 6:9), the resurrection of human bodies will be delayed until the end of the world when the heavenly movement will cease. For this reason, too, certain philosophers, who held that the movement of the heavens will never cease, maintained that human souls will return to mortal bodies such as we have now--whether, as Empedocles, they stated that the soul would return to the same body at the end of the great year, or that it would return to another body; thus Pythagoras asserted that "any soul will enter any body," as stated in De Anima i, 3.
Reply to Objection 1. Although the head is more conformed to the members by conformity of proportion (which is requisite in order that it have influence over the members) than one member is to another, yet the head has a certain causality over the members which the members have not; and in this the members differ from the head and agree with one another. Hence Christ's resurrection is an exemplar of ours, and through our faith therein there arises in us the hope of our own resurrection. But the resurrection of one of Christ's members is not the cause of the resurrection of other members, and consequently Christ's resurrection had to precede the resurrection of others who have all to rise again at the consummation of the world.
Reply to Objection 2. Although among the members some rank higher than others and are more conformed to the Head, they do not attain to the character of headship so as to be the cause of others. Consequently greater conformity to Christ does not give them a right to rise again before others as though they were exemplar and the others exemplate, as we have said in reference to Christ's resurrection: and if it has been granted to others that their resurrection should not be delayed until the general resurrection, this has been by special privilege of grace, and not as due on account of conformity to Christ.
Reply to Objection 3. Jerome, in a sermon on the Assumption [Ep. x ad Paul. et Eustoch., now recognized as spurious], seems to be doubtful of this resurrection of the saints with Christ, namely as to whether, having been witnesses to the resurrection, they died again, so that theirs was a resuscitation (as in the case of Lazarus who died again) rather than a resurrection such as will be at the end of the world--or really rose again to immortal life, to live for ever in the body, and to ascend bodily into heaven with Christ, as a gloss says on Matthew 27:52. The latter seems more probable, because, as Jerome says, in order that they might bear true witness to Christ's true resurrection, it was fitting that they should truly rise again. Nor was their resurrection hastened for their sake, but for the sake of bearing witness to Christ's resurrection: and that by bearing witness thereto they might lay the foundation of the faith of the New Testament: wherefore it was more fitting that it should be borne by the fathers of the Old Testament, than by those who died after the foundation of the New. It must, however, be observed that, although the Gospel mentions their resurrection before Christ's, we must take this statement as made in anticipation, as is often the case with writers of history. For none rose again with a true resurrection before Christ, since He is the "first-fruits of them that sleep" (1 Corinthians 15:20), although some were resuscitated before Christ's resurrection, as in the case of Lazarus.
Reply to Objection 4. On account of these words, as Augustine relates (De Civ. Dei xx, 7), certain heretics asserted that there will be a first resurrection of the dead that they may reign with Christ on earth for a thousand years; whence they were called "chiliasts" or "millenarians." Hence Augustine says (De Civ. Dei xx, 7) that these words are to be understood otherwise, namely of the spiritual resurrection, whereby men shall rise again from their sins to the gift of grace: while the second resurrection is of bodies. The reign of Christ denotes the Church wherein not only martyrs but also the other elect reign, the part denoting the whole; or they reign with Christ in glory as regards all, special mention being made of the martyrs, because they especially reign after death who fought for the truth, even unto death. The number of a thousand years denotes not a fixed number, but the whole of the present time wherein the saints now reign with Christ, because the number 1,000 designates universality more than the number 100, since 100 is the square of 10, whereas 1,000 is a cube resulting from the multiplication of ten by its square, for 10 X 10 = 100, and 100 X 10 = 1,000. Again in Psalm 104:8, "The word which He commanded to a thousand," i.e. all, "generations."
Source: Summa Theologica (New Advent)