As we begin Holy week, we see in the Liturgy a prime example of how fickle man can be. At the beginning of the week, the crowds are cheering as Our Lord enters the Holy City for the last time. They strew their cloaks on the ground before Him, and wave palm branches, shouting Hosanna Filio David, Rex Israel! Benedictus qui venit in nomine Domini, Hosanna in excelsis! At the end of the week they are shouting Crucifige eum!
On Palm Sunday, we receive palm branches, which are blessed. They are a sacramental, that is to remind us that we wish to be in the former crowd, not the latter. By our works, we shout either Hosanna to the Son of David or Crucify Him. Sacramentals help us to be more open to the grace of God. The Church, in her wisdom, has established many sacramentals to aid the Christian Faithful in their journey to eternal life. One would be foolish to leave these tools of our salvation unused.
As Our Lord neared death, according to St John, he said consummatum est, as the Latin reads. The English translation does not do justice to this. There is nuptual imagery used here, consumation, by which the couple seals their marriage. The death on the Cross is the act by which our Divine Bridegroom sealed His marriage covenant with His Bride, the Church. There is also the connection to consume -- Christ, according to St Paul, takes up all history in Himself. He sanctifies all creation.
Many non-Catholics will use this passage to condemn the Sacrifice of the Mass. Of course, this is wrong, because they don't understand what they are condemning in the first place (they don't really know the Catholic teaching), and in the second place, they don't understand memorial.
In the Jewish understanding of memorial, it means more than just to commemorate or call to mind something or someone. When pious Jews celebrate the Passover, they understand that through that liturgical meal, God is making present the very events of their salvation from slavery in Egypt. They aren't just reminding one another about it! In the context of that celebration (probably anticipated), Christ establishes the Holy Sacrifice of the Mass, commanding His Apostles Do this in memory of me.
The gift Christ gave to us in the Eucharist, through the gift of the Priesthood, is the ability to make present the events of our salvation. While celebrating the Passover for the last time, He transforms it and shows it to be a prefiguring of what He was to do. He then gives the power to His Apostles, who have handed it down through the generations, until He comes, to make the events of our salvation present in every time and place. The Jews knew that God transcends time and space, and is able to make events that are far distant present to us today.
When we celebrate the Mass, we are truly standing on the hill of Golgatha; we are peering with Sts Peter and John into the empty tomb; we are standing with the others on the Mount of Olives as He ascends! Imagine! Some think Mass is boring!
It is finished! At the same time, by the gift of the Eucharist, it continues through time and space to our present day, in our own town.