To the average Evangelical Protestant, Catholic Mass is the equivalent of a regular Sunday church service. The gathering is held at the same time & it employs prayer, worship & the Word, so its essentially the same, right?
Not so fast. The Mass is not like your ordinary Protestant service, but not for reasons one might think. The Mass is specifically a Memorial- a remembrance of Christ's Sacrifice for us at Calvary. Its much like the way we remember our nation's history. We recall something that has happened because it has somehow shaped who we are today. However, the Mass is not only a Memorial, but a kind of transcendence of time & place itself. When the Sacrifice (the Body & Blood of Christ) is presented on the altar, the boundaries of time disappear. All at once, we are transported to the night of the last supper, to the cross & to the tomb. A proclamation of the Mystery of Faith declares "Alleluia! Christ has died, Christ has risen, Christ shall come again!" While the Sacrifice is offered over & over at every Mass, its not a new Sacrifice- its the very same one Jesus offered some 2,000 years ago. How can this be?
Consider the American tradition of Thanksgiving, now nearly 400 years old. Thanksgiving was an event that happened once, but is still celebrated to this day. In a way, we return to the 1st Thanksgiving each time we offer our thanks for God's provision. The feast is repeated, but the spirit & purpose behind it remains the same. We are essentially "transported" back in time, ultimately transcending time itself as we feast with our ancestors. We are joined as "one" people in this act of thanksgiving, just as we are joined as "one body" in the act of Christ's Sacrifice.
Christians are called the Body of Christ for a reason. Just as He calls us to join in that 1st sacrifice through the Mass, we now offer ourselves up along with Him as living sacrifices. As we partake of the "Supper of the Lord", we are joined with His Body both as it was given for us that day- once, for all- & today, having become the "Mystical" Body of Christ, that is, the Church.