Jesus' Triumphal Entry, the Descent into Hell, and the Coming of the Messiah (Palm Sunday, Year A) 
On this coming Sunday, the Church will bring us to what may be one of my favorite Masses and my favorite sets of Scripture readings in the entire liturgical year: Palm Sunday of the Passion of the Lord, popularly known simply as ‘Palm Sunday’.
With the Palm Sunday readings, the Church ushers us into the climax of the liturgical year in the celebration of Holy Week. This is the last Sunday feast before the beginning of the Triduum, which will climax in the celebration of Easter (Latin Pascha), what the Catechism calls the “feast of feasts” (CCC 1169).
As you may recall—especially if you have young children who need to be held the entire time the Gospel is being proclaimed!—this is one of the longest sets of readings in the entire liturgical year. (A word of advice: don't lock your knees :) For on this Sunday, the Church not only commemorates the Triumphal Entry of Jesus into Jerusalem six days before the Passover; she also lays before the faithful the complete account of Jesus’ Passion and death, according to one of the Synoptic Gospels (This year, Year A, it is Matthew’s account.)
Given the sheer number and length of readings for this Sunday, it should go without saying that I can’t give a full analysis of them all. (Whole books have been written just on the Passion! In fact, I just published one myself.) Instead, I simply want to focus our attention on the Jewish roots of Jesus' Triumphal Entry, and show how Jesus fulfills Zechariah's prophecy of the Messiah in his Triumphal Entry, the Last Supper, his Passion, and even his descent into Hell.
Jesus Fulfills Zechariah's Prophecy of the Coming of the Messiah
Unlike other Masses, Palm Sunday contains two proclamations of the Gospel. The first is from Matthew’s account of Jesus Triumphal Entry into Jerusalem:
When Jesus and the disciples drew near Jerusalem and came to Bethphage on the Mount of Olives, Jesus sent two disciples, saying to them, “Go into the village opposite you, and immediately you will find an ass tethered,and a colt with her. Untie them and bring them here to me. And if anyone should say anything to you, reply, ‘The master has need of them.’ Then he will send them at once.” This happened so that what had been spoken through the prophet might be fulfilled: 'Say to daughter Zion,“Behold, your king comes to you,meek and riding on an ass,and on a colt, the foal of a beast of burden.” The disciples went and did as Jesus had ordered them.They brought the ass and the colt and laid their cloaks over them, and he sat upon them.The very large crowd spread their cloaks on the road, while others cut branches from the trees and strewed them on the road. The crowds preceding him and those following kept crying out and saying: “Hosanna to the Son of David; blessed is the he who comes in the name of the Lord; hosanna in the highest.”And when he entered Jerusalem the whole city was shaken and asked, “Who is this?” And the crowds replied, “This is Jesus the prophet, from Nazareth in Galilee.” (Matthew 21:1-11; NAB)
What is the meaning of this mysterious action? Why does Jesus ride an ass into Jerusalem, and why does the crowd react in the way that they do?
As is fairly well known, by choosing to publicly mount and ride a “colt” into Jerusalem in the midst of the procession of so many Passover pilgrims into the city, Jesus is performing what scholars refer to as a prophetic sign—a symbolic act which is meant to both symbolize and set in motion some major event in the history of salvation. In this case, Jesus’ act of riding the colt into Jerusalem harks back to Zechariah’s prophecy of the advent of the Messiah—the long-awaited king of Israel—to the city of Jerusalem (see Zechariah 9:9).
The Messiah Delivers His People from the Realm of the Dead
However, there is more here than simply an implicitly messianic public act. For when we go back to the prophecy of Zechariah and read it in its full context, we discover something very mysterious--namely, that the Messiah not only rides an ass, but comes to deliver "captives" from the "waterless pit":
Rejoice greatly, O daughter of Zion! Shout aloud, O daughter of Jerusalem! Lo, your king comes to you; triumphant and victorious is he, humble and riding on an ass, on a colt the foal of an ass. I will cut off the chariot from Ephraim and the war horse from Jerusalem; and the battle bow shall be cut off, and he shall command peace to the nations; his dominion shall be from sea to sea, and from the River to the ends of the earth. As for you also, because of the blood of my covenant with you, I will set your captives free from the waterless pit. (Zechariah 9:10-11)
The first part of Zechariah's prophecy is pretty clear: the future king--also known as the Messiah--will come riding an ass. But what about the second part of the prophecy? Notice here that according to Zechariah, the king who rides the ass into Jerusalem will not deliver his people through the shedding of blood in battle, but through the mysterious “blood of the covenant,” which will somehow set captives free from "the Pit"--a common Old Testament expression for the realm of the dead (Zech 9:10-11).
Once again, this Old Testament background of Jesus’ Triumphal Entry on Palm Sunday ultimately points forward to what he will accomplish in his Passion. For in the words of Jesus at the Last Supper, we find a striking allusion to Zechariah’s prophecy:
While they were eating, Jesus took bread, said the blessing, broke it, and giving it to his disciples said, "Take and eat; this is my body." Then he took a cup, gave thanks, and gave it to them, saying, "Drink from it, all of you, for this is my blood of the covenant, which will be shed on behalf of many for the forgiveness of sins." (Matthew 26:26-28)
The Blood of the Covenant and the Messiah's Descent into Hell
In other words, by means of his Triumphal Entry, Jesus is signaling much more than just the fact that he is the Messiah.He is also signaling what kind of Messiah he will be, and by what means he will set his people free from captivity—not by the blood of warfare, but by the blood of the covenant, which he will pour out under the appearance of wine in the Upper Room and on the wood of the Cross on Good Friday. It is by means of this blood, poured out upon the Cross on Calvary, that he will lead the righteous from the shadows of the Pit, but into the glory of Paradise. Indeed, this is the whole point of Holy Saturday: Christ descends into the realm of the dead--Hades--to free the righteous from the realm of the dead. In the words of the Apostle Paul:
Therefore it is said, "When he ascended on high he led a host of captives, and he gave gifts to men." In saying, "He ascended," what does it mean but that he had also descended into the lower parts of the earth? He who descended is he who also ascended far above all the heavens, that he might fill all things. (Ephesians 4:8-10)
Who are the "host of captives" that Christ "led on high" when he ascended into heaven, after he "descended" to the dead? They are none other than the righteous dead of the Old Covenant, who were waiting for the Messiah to finally come triumphant to Jerusalem and her people. In the words of the Catechism of the Catholic Church:
Jesus did not descend into hell to deliver the damned, nor to destroy the hell of damnation, but to free the just who had gone before him. "The gospel was preached even to the dead." (1 Pet 4:6). The descent into hell brings the Gospel message of salvation to complete fulfillment. This is the last phase of Jesus' messianic mission, a phase which is condensed in time but vast in its real significance: the spread of Christ's redemptive work to all men of all times and all places... (CCC 633-634)
This is the real 'return from exile' that will be accomplished by the Messiah: he will lead the exiled children of Eve back to the Paradise of God through the blood of the new and everlasting covenant.
The Palm Branches and the Coming of the King to the Altar
Now, at this point, someone might ask: But how does he Jesus accomplish all this? What role does the Cross have to play? This question takes us back to the crowd’s response to Jesus’ triumphal entry, with their proclamation of the words::
"Hosanna to the Son of David; blessed is he who comes in the name of the Lord; hosanna in the highest!" (Matthew 21:9).
It is extremely important to recognize that the Jewish crowd is taking this chant for "salvation" (Hosanna means "Save" or "Give Salvation!") from Psalm 118, a popular song that was sung during the feasts of Passover and Tabernacles. However, once again, when we go back and look at the Psalm in context, we discover yet again several striking features of the king whose arrival is being celebrated:
Open to me the gates of righteousness, that I may enter through them and give thanks to the LORD… The stone which the builders rejected has become the head of the corner... Save us, we beseech thee, O LORD! O LORD, we beseech thee, give us success! Blessed be he who comes in the name of the LORD! We bless you from the house of the LORD. The LORD is God, and he has given us light! Bind the festal procession with branches, up to the horns of the altar! Thou art my God, and I will give thanks to thee.. (Psalm 118:19, 22, 25-28).
The critical point to notice here is that in Psalm 118, the king is not simply coming into the city (‘open to me the gates)—he is going up to the Temple to offer sacrifice. And not just any kind of sacrifice, but the “thanksgiving” sacrifice, known in Hebrew as the todah offering (see Leviticus 7).
Once this Old Testament background to the crowd’s response is in place, the deeper meaning of Jesus’ Triumphal Entry is revealed. The crowds with their branches and their Psalms have it right: Jesus is the king of Israel; he has come to his city; and he is going up to the altar to offer a sacrifice of thanksgiving. But the sacrifice he is going to offer is not that of bulls or goats, but of himself. And the todah that he will give will begin with the Eucharist celebrated in the Upper Room and consummated on the altar of the Cross.
The Messiah Still "Goes Up" to the Altar of the Eucharist
In other words, at every Mass, when we proclaim—“Blessed is He Who Comes in the Name of the Lord,Hosanna in the Highest!”—we are not only remembering the first Palm Sunday. Even more, we are celebration the liturgical coming of the King into our midst, as he 'ascends' to the altar of the Eucharist. As he said at the Last Supper, there he 'pours out' the blood of the new covenant in the one eternal offering by which we too are given peace and prepared to enter into the kingdom of Paradise. In the words of the Catechism of the Catholic Church:
How will Jerusalem welcome her Messiah? Although Jesus had always refused popular attempts to make him king, he chooses the time and prepares the details for his messianic entry into the city of "his father David". Acclaimed as son of David, as the one who brings salvation (Hosanna means "Save!" or "Give salvation!"), the "King of glory" enters his City "riding on an ass". Jesus conquers the Daughter of Zion, a figure of his Church, neither by ruse nor by violence, but by the humility that bears witness to the truth… Their acclamation, "Blessed be he who comes in the name of the Lord", is taken up by the Church in the "Sanctus" of the Eucharistic liturgy that introduces the memorial of the Lord's Passover.
Jesus' entry into Jerusalem manifested the coming of the kingdom that the King-Messiah was going to accomplish by the Passover of his Death and Resurrection. It is with the celebration of that entry on Palm Sunday that the Church's liturgy solemnly opens Holy Week. (CCC 559-560)