Can someone explain what exactly is the mystery of faith and also the purpose I the sign of peace
The Mystery of Faith is the Eucharist. The statement “The Mystery of Faith” is just that, a statement by the priest to the faithful about what has just happened on the altar. It is the final statement of the Eucharistic Prayer.
The problem is, the old translation led people to believe that what the priest was referring to was the Memorial Acclamation, which immediately follows the Mysterium Fidei
So: Mystery of Faith is the Eucharist
The Memorial Acclimation is what follows, and has three approved English versions
- We proclaim your Death, O Lord,and profess your Resurrection,until you come again
- When we eat this Bread and drink this Cup,we proclaim your Death, O Lord,until you come again.
- Save us, Saviour of the world,for by your Cross and Resurrectionyou have set us free.
As to your second point, the Sign of Peace is the priest, in persona Christi, sharing the Peace of Christ with us.
It involves the priest saying " The Peace of Christ be with you" and we respond “And with your Spirit”
That concludes the Signum Christi. There is an optional component, where members of the faithful are invited to extend a sing of the reception of the Peace of Christ with each other.
Again it is option, and it’s purpose to to signify to each other what we have received from the priest.