What follows is my rough translation from the Latin of ST 3.53.1. For another English translation, see the New Advent Summa; I borrowed a bit or two from that translation. I'll probably have several posts over this next week on this subject, and on other Holy Week subjects.
 So we proceed to the first [objection]. It seems that it was not necessary for Christ to rise again. Thus Damascene says (in book IV [of De Fid. Orth.]), "Resurrection is the rising again of what is disintegrated and fallen." But Christ did not fall through sin, nor was his body disintegrated, as is clear from what was said above (ST 3.51.3). Therefore it was not appropriate for him to rise.
 Further, whoever rises is promoted to something higher, because to rise (surgere) is to be uplifted (sursum moveri). But the body of Christ after death remained united to the divinity, and so could not be promoted to something higher. Therefore rising again was not due to it.
 Further, everything that happened to the humanity of Christ was ordered to our salvation. But the passion of Christ suffices for our salvation, for through it we are liberated from fault and penalty, as is clear from what was said above (ST 3.49.1,3). Therefore it was not necessary for Christ to rise from the dead.
But against this is what is said at the end of Luke, "It was needful that Christ suffer and rise from the dead."
I reply that it must be said that it was necessary for Christ to rise again, for five reasons.
First of all, for the commendation of divine justice, to which pertains exalting those who humble themselves for God's sake, according to Luke 1: "He deposes potentates from their seats and exalts the humble." Therefore because Christ, according to charity and obedience to God, humbled himself even to death on the cross, it was needful that he be exalted by God even to glorious resurrection, as it is said in His Person in the Psalm (138:2) as the Gloss expounds it, "You have known," that is, approved, "my sitting down," that is, humility and passion, "and my rising up," that is, glorification in resurrection."
Second, for our instruction in faith. Because through his resurrection our faith about Christ's divinity is confirmed, because, as is said at the end of II Corinthians, "Although he was crucified from our infirmity, he lives from God's power." And likewise, it is said in I Corinthians 15, If Christ did not rise, our preaching is empty, and our faith is empty." And in the Psalm (29:10), "What profit is in my blood," that is, in the shedding of my blood, "while I descend," as it were through various grades of evil, "into corruption?" As though He were to answer, "None, If therefore I do not rise again at once, an my body be decayed, I shall bring news to no one, I shall profit no one," as the Gloss expounds.
Third, for the uplifting of our hope. Because, while we see Christ, who is our Head, rise again, we also hope in our own resurrection. Wherefore it is said in I Corinthians 15, "If Christ is preached that He rises from the dead, how is it said among you that there is no resurrection of the dead?" And in Job 19 it is said, "I know," that is, through the certainty of faith, "that my redeemer," that is, Christ, "lives," having risen from the dead, and therefore "in the last day, I shall rise out of the earth; this my hope is stored in my bosom."
Fourth, for the formation (informationem) of the lives of the faithful, according to which [it is said in] Romans 6, "As Christ is risen from the dead throught the glory of the Father, even so may we walk in newness of life." And further down, "Christ, rising from the dead, therefore no longer dies; so also recognize that you are dead to sin, but living to God.
Fifth, for the completion of our salvation. Because just as for this reason he endured evil things in dying so that he might liberate us from evil, so he is glorified in rising again so that he might promote us to good, according to Romans 4, "He was delivered for our sins, and he rose for our justification."
To the first it must therefore be said that, although Christ did not fall through sin, He fell through death, because as sin is a fall from justice, so death is a fall from life. Wherefore we can understand as from the person of Christ what is said in Micah 7, "Do no rejoice over me, my enemy, because I have fallen; I will rise." Likewise, although Christ's body was not disintegrated through returning to dust, yet the separation of the soul from the body was a sort of disintegration.
To the second it must be said that divinity was united to the flesh of Christ after death by a personal union, not a union of nature, as the soul is united to the body as form so as to constitute human nature. And because of this, the body, united with the soul, was promoted to a higher state of nature, but not to a higher personal state.
To the third it must be said that the passion of Christ operated for our salvation, properly speaking, inasmuch as it removed evils; but resurrection inasmuch as it was the first beginning and exemplar of goods.