[Recently there has been a discussion in the comments section about whether or not the sign of peace between the laity is mandatory or optional. Fr. McNamara gives his interpretation:]
ROME, JULY 11, 2006 (Zenit.org).- Answered by Father Edward McNamara, professor of liturgy at the Regina Apostolorum university.
Q: Does the rubric "The priest or deacon may say, 'Let us offer the sign of peace'" still mean the exchange between the people, rather than that between priest and people? I am informed that the people may never omit this exchange between themselves, even if the invitation to do so is not given. -- G.D., Thornley, England
A: The theme of the rite of peace (or "kiss of peace") is dealt with in several places in the General Instruction of the Roman Missal. While giving an overall description of the rites of Mass, it says in No. 82:
"The Rite of Peace follows, by which the Church asks for peace and unity for herself and for the whole human family, and the faithful express to each other their ecclesial communion and mutual charity before communicating in the Sacrament.
"As for the sign of peace to be given, the manner is to be established by Conferences of Bishops in accordance with the culture and customs of the peoples. It is, however, appropriate that each person offer the sign of peace only to those who are nearest and in a sober manner."
Later, when describing the various forms of rite, it adds more details. Describing Mass with a priest, it says in No. 154:
"Then the priest, with hands extended, says aloud the prayer, 'Domine Iesu Christe, qui dixisti' (Lord Jesus Christ, you said). After this prayer is concluded, extending and then joining his hands, he gives the greeting of peace while facing the people and saying, 'Pax Domini sit semper vobiscum' (The peace of the Lord be with you always). The people answer, 'Et cum spiritu tuo' (And also with you). Afterwards, when appropriate, the priest adds, 'Offerte vobis pacem' (Let us offer each other the sign of peace).
"The priest may give the sign of peace to the ministers but always remains within the sanctuary, so as not to disturb the celebration. In the dioceses of the United States of America, for a good reason, on special occasions (for example, in the case of a funeral, a wedding, or when civic leaders are present) the priest may offer the sign of peace to a few of the faithful near the sanctuary. At the same time, in accord with the decisions of the Conference of Bishops, all offer one another a sign that expresses peace, communion, and charity. While the sign of peace is being given, one may say, 'Pax Domini sit semper vobiscum' (The peace of the Lord be with you always), to which the response is Amen."
No. 181 covers the situation when a deacon is present and No. 239 describes concelebrations:
"181: After the priest has said the prayer at the Rite of Peace and the greeting 'Pax Domini sit semper vobiscum' (The peace of the Lord be with you always) and the people have responded, 'Et cum spiritu tuo' (And also with you), the deacon, if it is appropriate, invites all to exchange the sign of peace. He faces the people and, with hands joined, says, 'Offerte vobis pacem pacem' (Let us offer each other the sign of peace). Then he himself receives the sign of peace from the priest and may offer it to those other ministers who are closer to him.
"239: After the deacon or, when no deacon is present, one of the concelebrants has said the invitation 'Offerte vobis pacem pacem' (Let us offer each other the sign of peace), all exchange the sign of peace with one another. The concelebrants who are nearer the principal celebrant receive the sign of peace from him before the deacon does."
Finally, "Redemptionis Sacramentum," No. 71, adds a further note: "The practice of the Roman Rite is to be maintained according to which the peace is extended shortly before Holy Communion. For according to the tradition of the Roman Rite, this practice does not have the connotation either of reconciliation or of a remission of sins, but instead signifies peace, communion and charity before the reception of the Most Holy Eucharist. It is rather the Penitential Act to be carried out at the beginning of Mass (especially in its first form) which has the character of reconciliation among brothers and sisters."
These documents show that both the invitation and actual exchange of peace form part of a single act and are done "if it is appropriate." If for some good reason the celebrant decides to omit the invitation, then the faithful are not required to exchange the sign of peace among themselves.
"Redemptionis Sacramentum" highlights another reason. The peace exchanged is the Lord's peace coming from the sacrifice of the altar. An exchange of the sign of peace without an invitation from the altar in a way changes the symbolic value of the rite and could reduce it to signify merely human benevolence.
All the same, pastorally speaking, it is preferable to have some stability in using or omitting the invitation to the sign of peace. If a priest occasionally or irregularly omits the rite he will probably find that the faithful start shaking hands anyway from force of habit. This can lead to confusion.
Some priests omit it for weekday Masses, others include it always. There is no absolute criterion for all cases.