In most eucharistic liturgies, a formal invitation to receive the body and blood of Christ takes place after the breaking of the bread and the pouring of the cups. One of the popular forms used in the east is “Holy things for God’s holy people!”
In the Roman Catholic Church the words of this invitation and our response is inspired by scripture. The priest holds up the sacred species and says, “This is the Lamb of God who takes away the sins of the world” (John 1:29) to which is added, “Happy are those who are called to the supper of the lamb.” (Revelation 19:9).
Then the priest and the assembly respond together: “Lord, I am not worthy that you should enter under my roof, but only say the word and my soul shall be healed” (Matthew 8:9).
The present Roman form strikes a balance between a worthiness rooted in baptism and a humility possessed by the centurion. The assembly is invited to look at the Eucharistic bread and to express reverence, confidence, and faith.
(Adapted from, The Mystery of Faith, FDLC)