**OREMUS (LET US PRAY).** – A general invitation in the Roman Rite pronounced by the officiant to the faithful before prayers in the Mass (Collect, Secret, Postcommunion, Our Father), in the Divine Office, and on other occasions.
On Good Friday, the *O.* is followed by a brief allocution specifying the intention of the prayer: *«Oremus, dilectissimi nobis, pro Ecclesia... pro Papa... ut Deus purget... auferat... indulgeat.»* To this invitation, more or less detailed, corresponded a prayer of the people, and in fact until the 9th century (Cod. Vat. Ottobon. 313, in H. Lietzmann, *Das Sacramentarium Gregorianum*, Münster in V., 1921, p. 79, n. 9) a few moments of silent prayer followed. Outside of Easter, on weekdays or days of penance, the people knelt at the deacon’s announcement *«Flectamus genua»*; then, at a second announcement *«Levate»*, they rose. The priest, as on feast days, after a moment of prayer, would gather aloud the common sentiments of the faithful into a brief prayer, later called the "Collect," to which the people responded with *«Amen.»* Gradually, this invitation was shortened, and the subsequent interval of silent prayer omitted, so that the *O.* became a simple introductory formula, immediately followed by the priest’s prayer. The ancient formula remains in the weekday Masses of the Ember Days, Good Friday, and the Easter Vigil. In the Ambrosian Rite, the invitation *O.* is never used in the Collect. In the Gallican liturgy, the first Collect of the day is preceded by a more or less lengthy Preface, sometimes in the form of a short homily delivered by the bishop to invite to prayer and explain the day’s feast; the invitations for the other prayers are unknown, though perhaps the *O.* was used, as in the Roman Rite. (L. Duchesne, *Origines du culte chrétien*, Paris 1925, p. 113). The Mozarabic liturgy, instead, uses the *O.* twice, before the *Agyos* and the Our Father. In the Eastern rites, the invitation, pronounced by the deacon, is always followed by a response from the people, *«Kyrie eleison»* or similar. The invitation, sometimes as simple as in the Roman Rite, is more detailed and specific, especially in the so-called prayer of the faithful. During the deacon’s prayer with the people, the prayer is recited by the priest (Byzantine Rite). In practical usage, the word *O.* also came to signify the entire following prayer to be said according to the occasion.
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J. A. Jungmann, *Missarum sollemnia*, I, Vicenza 1949, pp. 452–56;
M. Righetti, *Manuale di storia liturgica*, I, 2nd ed., Milano 1950, pp. 202–203; III, ibid. 1949, p. 182.