Objection 1. It would seem that Christ did not suffer at a suitable time. For Christ's Passion was prefigured by the sacrifice of the Paschal lamb: hence the Apostle says (1 Corinthians 5:7): "Christ our Pasch is sacrificed." But the paschal lamb was slain "on the fourteenth day at eventide," as is stated in Exodus 12:6. Therefore it seems that Christ ought to have suffered then; which is manifestly false: for He was then celebrating the Pasch with His disciples, according to Mark's account (14:12): "On the first day of the unleavened bread, when they sacrificed the Pasch"; whereas it was on the following day that He suffered.
Objection 2. Further, Christ's Passion is called His uplifting, according to John 3:14: "So must the Son of man be lifted up." And Christ is Himself called the Sun of Justice, as we read Malachi 4:2. Therefore it seems that He ought to have suffered at the sixth hour, when the sun is at its highest point, and yet the contrary appears from Mark 15:25: "It was the third hour, and they crucified Him."
Objection 3. Further, as the sun is at its highest point in each day at the sixth hour, so also it reaches its highest point in every year at the summer solstice. Therefore Christ ought to have suffered about the time of the summer solstice rather than about the vernal equinox.
Objection 4. Further, the world was enlightened by Christ's presence in it, according to John 9:5: "As long as I am in the world I am the light of the world." Consequently it was fitting for man's salvation that Christ should have lived longer in the world, so that He should have suffered, not in young, but in old, age.
On the contrary, It is written (John 13:1): "Jesus, knowing that His hour was come for Him to pass out of this world to the Father"; and (John 2:4): "My hour is not yet come." Upon which texts Augustine observes: "When He had done as much as He deemed sufficient, then came His hour, not of necessity, but of will, not of condition, but of power." Therefore Christ died at an opportune time.
I answer that, As was observed above (Article 1), Christ's Passion was subject to His will. But His will was ruled by the Divine wisdom which "ordereth all things" conveniently and "sweetly" (Wisdom 8:1). Consequently it must be said that Christ's Passion was enacted at an opportune time. Hence it is written in De Qq. Vet. et Nov. Test., qu. lv: "The Saviour did everything in its proper place and season."
Reply to Objection 1. Some hold that Christ did die on the fourteenth day of the moon, when the Jews sacrificed the Pasch: hence it is stated (John 18:28) that the Jews "went not into Pilate's hall" on the day of the Passion, "that they might not be defiled, but that they might eat the Pasch." Upon this Chrysostom observes (Hom. lxxxii in Joan.): "The Jews celebrated the Pasch then; but He celebrated the Pasch on the previous day, reserving His own slaying until the Friday, when the old Pasch was kept." And this appears to tally with the statement (John 13:1-5) that "before the festival day of the Pasch... when supper was done"... Christ washed "the feet of the disciples."
But Matthew's account (26:17) seems opposed to this; that "on the first day of the Azymes the disciples came to Jesus, saying: Where wilt Thou that we prepare for Thee to eat the Pasch?" From which, as Jerome says, "since the fourteenth day of the first month is called the day of the Azymes, when the lamb was slain, and when it was full moon," it is quite clear that Christ kept the supper on the fourteenth and died on the fifteenth. And this comes out more clearly from Mark 14:12: "On the first day of the unleavened bread, when they sacrificed the Pasch," etc.; and from Luke 22:7: "The day of the unleavened bread came, on which it was necessary that the Pasch should be killed."
Consequently, then, others say that Christ ate the Pasch with His disciples on the proper day--that is, on the fourteenth day of the moon--"showing thereby that up to the last day He was not opposed to the law," as Chrysostom says (Hom. lxxxi in Matth.): but that the Jews, being busied in compassing Christ's death against the law, put off celebrating the Pasch until the following day. And on this account it is said of them that on the day of Christ's Passion they were unwilling to enter Pilate's hall, "that they might not be defiled, but that they might eat the Pasch."
But even this solution does not tally with Mark, who says: "On the first day of the unleavened bread, when they sacrificed the Pasch." Consequently Christ and the Jews celebrated the ancient Pasch at the one time. And as Bede says on Luke 22:7-8: "Although Christ who is our Pasch was slain on the following day--that is, on the fifteenth day of the moon--nevertheless, on the night when the Lamb was sacrificed, delivering to the disciples to be celebrated, the mysteries of His body and blood, and being held and bound by the Jews, He hallowed the opening of His own immolation--that is, of His Passion."
But the words (John 13:1) "Before the festival day of the Pasch" are to be understood to refer to the fourteenth day of the moon, which then fell upon the Thursday: for the fifteenth day of the moon was the most solemn day of the Pasch with the Jews: and so the same day which John calls "before the festival day of the Pasch," on account of the natural distinction of days, Matthew calls the first day of the unleavened bread, because, according to the rite of the Jewish festivity, the solemnity began from the evening of the preceding day. When it is said, then, that they were going to eat the Pasch on the fifteenth day of the month, it is to be understood that the Pasch there is not called the Paschal lamb, which was sacrificed on the fourteenth day, but the Paschal food--that is, the unleavened bread--which had to be eaten by the clean. Hence Chrysostom in the same passage gives another explanation, that the Pasch can be taken as meaning the whole feast of the Jews, which lasted seven days.
Reply to Objection 2. As Augustine says (De Consensu Evang. iii): "'It was about the sixth hour' when the Lord was delivered up by Pilate to be crucified," as John relates. For it "was not quite the sixth hour, but about the sixth--that is, it was after the fifth, and when part of the sixth had been entered upon until the sixth hour was ended--that the darkness began, when Christ hung upon the cross. It is understood to have been the third hour when the Jews clamored for the Lord to be crucified: and it is most clearly shown that they crucified Him when they clamored out. Therefore, lest anyone might divert the thought of so great a crime from the Jews to the soldiers, he says: 'It was the third hour, and they crucified Him,' that they before all may be found to have crucified Him, who at the third hour clamored for His crucifixion. Although there are not wanting some persons who wish the Parasceve to be understood as the third hour, which John recalls, saying: 'It was the Parasceve, about the sixth hour.' For 'Parasceve' is interpreted 'preparation.' But the true Pasch, which was celebrated in the Lord's Passion, began to be prepared from the ninth hour of the night--namely, when the chief priests said: 'He is deserving of death.'" According to John, then, "the sixth hour of the Parasceve" lasts from that hour of the night down to Christ's crucifixion; while, according to Mark, it is the third hour of the day.
Still, there are some who contend that this discrepancy is due to the error of a Greek transcriber: since the characters employed by them to represent 3 and 6 are somewhat alike.
Reply to Objection 3. According to the author of De Qq. Vet. et Nov. Test., qu. lv, "our Lord willed to redeem and reform the world by His Passion, at the time of year at which He had created it--that is, at the equinox. It is then that day grows upon night; because by our Saviour's Passion we are brought from darkness to light." And since the perfect enlightening will come about at Christ's second coming, therefore the season of His second coming is compared (Matthew 24:32-33) to the summer in these words: "When the branch thereof is now tender, and the leaves come forth, you know that summer is nigh: so you also, when you shall see all these things, know ye that it is nigh even at the doors." And then also shall be Christ's greatest exaltation.
Reply to Objection 4. Christ willed to suffer while yet young, for three reasons. First of all, to commend the more His love by giving up His life for us when He was in His most perfect state of life. Secondly, because it was not becoming for Him to show any decay of nature nor to be subject to disease, as stated above (Question 14, Article 4). Thirdly, that by dying and rising at an early age Christ might exhibit beforehand in His own person the future condition of those who rise again. Hence it is written (Ephesians 4:13): "Until we all meet into the unity of faith, and of the knowledge of the Son of God, unto a perfect man, unto the measure of the age of the fulness of Christ."
Source: Summa Theologica (New Advent)