Following the words of Consecration ("THIS IS MY BODY," etc) we have the next dialogue between the priest and the people: mysterium fidei, ‘The mystery of faith.’
This part of the Mass is both very new and very old. It is old because the phrase, “mysterium fidei,” actually used to be part of the consecration formula. It is not a Scriptural phrase, unlike the rest of the words of consecration, which is probably why the Church decided to take it out of the formula and yet retain it in the making of this new priest-congregation response. In doing so, the Church gave us a beautiful new moment in the Mass.
There are three options for the people’s part that follows after the priest says or sings, “The mystery of faith.”
“When we eat this bread and drink this cup, we proclaim your death O Lord, until you come again.”
“We proclaim your death O Lord and profess your resurrection until you come again.”
“Save us savior of the world for by your cross and resurrection you have set us free.”
So, what is going on here? First, let’s look at an interesting thing from the Order of Mass (an instruction manual for the Mass.) It says,” Then [the priest] says, “The mystery of faith,” and the people continue, acclaiming…” This sounds un-extraordinary at first but notice both the distinction and connection between the people and the priest. The priest is not supposed to say the people’s response. At Mass, you will see me sing the Gloria and the Sanctus and other parts, but you will never see me join you all for the memorial acclamation (unless I get distracted). And yet, the people ‘continue’ what the priest started. It is not a response to his statement as much as it is the continuation of it. So, there is both a connection/continuation and a distinction/separation.
The word mystery ('mysterium' in latin) comes from a root word “muo.” This word literally means, “to shut one’s mouth,” or to be dumbfounded. Our faith has a long history with the word mysterium. It is essential to our belief that our God is far more wonderful than we can ever imagine, and in the face of many elements of divine revelation, when we have gone as far as we can go with our human words and intellects, we must stop and sit in silence and wonder at the great mystery handed to us. The Eucharist is the center, source, and summit of our faith and all the mysteries. And so, the job of the priest at that moment, having just confected the bread and wine into the body and blood of Christ, is to ‘step back’ in recognition of the miracle before him. He says, “The mystery of faith,” and then just stands in awe. It is the ‘job’ of the people to then give what words we can to this great mystery.
And what are these words? When in doubt, we (the Church) always go to Scripture. The first two options spring from 1 Corinthians 11:26: “For as often as you eat this bread and drink the cup, you proclaim the death of the Lord until he comes.”
The third option is rooted in John 4:22, though the connection is less significant: “We no longer believe just because of what you said; now we have heard for ourselves, and we know that this man really is the Savior of the world.”
And so, considering the Scriptural origins and the adaptation of making them into responses at Mass, we see a few themes. First, they acknowledge the presence of Christ. What was just bread and wine is now Jesus. Second, they connect us to the root purpose of the Mass and the Eucharist: to unite us to our saving Lord, especially with respect to the Grace of his mortal Sacrifice through which we also hope to participate in his resurrection. Third, they acknowledge our faith in the past and our hope for the future, the lynchpin of both of which is the Eucharist. All told, the people are not only recognizing the ‘real presence’ of Christ. They are also recognizing the mystery of the whole Eucharistic Sacrifice.