Objection 1. It would seem that the resurrection of Christ is not the cause of our resurrection. For, given the cause, the effect follows. Yet given the resurrection of Christ the resurrection of the other dead did not follow at once. Therefore His resurrection is not the cause of ours.
Objection 2. Further, an effect cannot be unless the cause precede. But the resurrection of the dead would be even if Christ had not risen again: for God could have delivered man in some other way. Therefore Christ's resurrection is not the cause of ours.
Objection 3. Further, the same thing produces the one effect throughout the one same species. Now the resurrection will be common to all men. Since then Christ's resurrection is not its own cause, it is not the cause of the resurrection of others.
Objection 4. Further, an effect retains some likeness to its cause. But the resurrection, at least of some, namely the wicked, bears no likeness to the resurrection of Christ. Therefore Christ's resurrection will not be the cause of theirs.
On the contrary, "In every genus that which is first is the cause of those that come after it" (Metaph. ii, 1). Now Christ, by reason of His bodily resurrection, is called "the first-fruits of them that sleep" (1 Corinthians 15:20), and "the first-begotten of the dead" (Apocalypse 1:5). Therefore His resurrection is the cause of the resurrection of others.
Further, Christ's resurrection has more in common with our bodily resurrection than with our spiritual resurrection which is by justification. But Christ's resurrection is the cause of our justification, as appears from Romans 4:25, where it is said that He "rose again for our justification." Therefore Christ's resurrection is the cause of our bodily resurrection.
I answer that, Christ by reason of His nature is called the mediator of God and men: wherefore the Divine gifts are bestowed on men by means of Christ's humanity. Now just as we cannot be delivered from spiritual death save by the gift of grace bestowed by God, so neither can we be delivered from bodily death except by resurrection wrought by the Divine power. And therefore as Christ, in respect of His human nature, received the firstfruits of grace from above, and His grace is the cause of our grace, because "of His fulness we all have received... grace for grace" (John 1:16), so in Christ has our resurrection begun, and His resurrection is the cause of ours. Thus Christ as God is, as it were, the equivocal cause of our resurrection, but as God and man rising again, He is the proximate and, so to say, the univocal cause of our resurrection. Now a univocal efficient cause produces its effect in likeness to its own form, so that not only is it an efficient, but also an exemplar cause in relation to that effect. This happens in two ways. For sometimes this very form, whereby the agent is likened to its effect, is the direct principle of the action by which the effect is produced, as heat in the fire that heats: and sometimes it is not the form in respect of which this likeness is observed, that is primarily and directly the principle of that action, but the principles of that form. For instance, if a white man beget a white man, the whiteness of the begetter is not the principle of active generation, and yet the whiteness of the begetter is said to be the cause of the whiteness of the begotten, because the principles of whiteness in the begetter are the generative principles causing whiteness in the begotten. In this way the resurrection of Christ is the cause of our resurrection, because the same thing that wrought the resurrection of Christ, which is the univocal efficient cause of our resurrection, is the active cause of our resurrection, namely the power of Christ's Godhead which is common to Him and the Father. Hence it is written (Romans 8:11): "He that raised up Jesus Christ from the dead shall quicken also your mortal bodies." And this very resurrection of Christ by virtue of His indwelling Godhead is the quasi-instrumental cause of our resurrection: since the Divine operations were wrought by means of Christ's flesh, as though it were a kind of organ; thus the Damascene instances as an example (De Fide Orth. iii, 15) the touch of His body whereby He healed the leper (Matthew 8:3).
Reply to Objection 1. A sufficient cause produces at once its effect to which it is immediately directed, but not the effect to which it is directed by means of something else, no matter how sufficient it may be: thus heat, however intense it be, does not cause heat at once in the first instant, but it begins at once to set up a movement towards heat, because heat is its effect by means of movement. Now Christ's resurrection is said to be the cause of ours, in that it works our resurrection, not immediately, but by means of its principle, namely the Divine power which will work our resurrection in likeness to the resurrection of Christ. Now God's power works by means of His will which is nearest to the effect; hence it is not necessary that our resurrection should follow straightway after He has wrought the resurrection of Christ, but that it should happen at the time which God's will has decreed.
Reply to Objection 2. God's power is not tied to any particular second causes, but that He can produce their effects either immediately or by means of other causes: thus He might work the generation of lower bodies even though there were no movement of the heaven: and yet according to the order which He has established in things, the movement of the heaven is the cause of the generation of the lower bodies. In like manner according to the order appointed to human things by Divine providence, Christ's resurrection is the cause of ours: and yet He could have appointed another order, and then our resurrection would have had another cause ordained by God.
Reply to Objection 3. This argument holds when all the things of one species have the same order to the first cause of the effect to be produced in the whole of that species. But it is not so in the case in point, because Christ's humanity is nearer to His Godhead, Whose power is the first cause of the resurrection, than is the humanity of others. Hence Christ's Godhead caused His resurrection immediately, but it causes the resurrection of others by means of Christ-man rising again.
Reply to Objection 4. The resurrection of all men will bear some resemblance to Christ's resurrection, as regards that which pertains to the life of nature, in respect of which all were conformed to Christ. Hence all will rise again to immortal life; but in the saints who were conformed to Christ by grace, there will be conformity as to things pertaining to glory.
Source: Summa Theologica (New Advent)