I answer that, It was not fitting for Christ's body to putrefy, or in any way be reduced to dust, since the putrefaction of any body comes of that body's infirmity of nature, which can no longer hold the body together. But as was said above (Q. 50, A. 1, ad 2), Christ's death ought not to come from weakness of nature, lest it might not be believed to be voluntary: and therefore He willed to die, not from sickness, but from suffering inflicted on Him, to which He gave Himself up willingly. And therefore, lest His death might be ascribed to infirmity of nature, Christ did not wish His body to putrefy in any way or dissolve no matter how; but for the manifestation of His Divine power He willed that His body should continue incorrupt. Hence Chrysostom says (Cont. Jud. et Gent. quod 'Christus sit Deus') that "with other men, especially with such as have wrought strenuously, their deeds shine forth in their lifetime; but as soon as they die, their deeds go with them. But it is quite the contrary with Christ: because previous to the cross all is sadness and weakness, but as soon as He is crucified, everything comes to light, in order that you may learn it was not an ordinary man that was crucified."
Reply Obj. 1: Since Christ was not subject to sin, neither was He prone to die or to return to dust. Yet of His own will He endured death for our salvation, for the reasons alleged above (Q. 51, A. 1). But had His body putrefied or dissolved, this fact would have been detrimental to man's salvation, for it would not have seemed credible that the Divine power was in Him. Hence it is on His behalf that it is written (Ps. 19:10): "What profit is there in my blood, whilst I go down to corruption?" as if He were to say: "If My body corrupt, the profit of the blood shed will be lost."
Reply Obj. 2: Christ's body was a subject of corruption according to the condition of its passible nature, but not as to the deserving cause of putrefaction, which is sin: but the Divine power preserved Christ's body from putrefying, just as it raised it up from death.
Reply Obj. 3: Christ rose from the tomb by Divine power, which is not narrowed within bounds. Consequently, His rising from the grave was a sufficient argument to prove that men are to be raised up by Divine power, not only from their graves, but also from any dust whatever. _______________________
FOURTH ARTICLE [III, Q. 51, Art. 4]
Whether Christ Was in the Tomb Only One Day and Two Nights?
Objection 1: It would seem that Christ was not in the tomb during only one day and two nights; because He said (Matt. 12:40): "As Jonas was in the whale's belly three days and three nights: so shall the Son of man be in the heart of the earth three days and three nights." But He was in the heart of the earth while He was in the grave. Therefore He was not in the tomb for only one day and two nights.
Obj. 2: Gregory says in a Paschal Homily (Hom. xxi): "As Samson carried off the gates of Gaza during the night, even so Christ rose in the night, taking away the gates of hell." But after rising He was not in the tomb. Therefore He was not two whole nights in the grave.
Obj. 3: Further, light prevailed over darkness by Christ's death. But night belongs to darkness, and day to light. Therefore it was more fitting for Christ's body to be in the tomb for two days and a night, rather than conversely.
On the contrary, Augustine says (De Trin. iv): "There were thirty-six hours from the evening of His burial to the dawn of the resurrection, that is, a whole night with a whole day, and a whole night."