Introit

The Introit (from Latin: introitus, "entrance") is part of the opening of the liturgical celebration of the Eucharist for many Christian denominations. In its most complete version, it consists of an antiphon, psalm verse and Gloria Patri that is spoken or sung at the beginning of the celebration. It is part of the Proper of the liturgy; that is, the part that changes over the liturgical year.

In the Roman Rite of the Roman Catholic Church it is known as the antiphona ad introitum (Entrance antiphon), as in the text for each day's Mass, or as the cantus ad introitum (Entrance chant) as in the General Instruction of the Roman Missal, 47 and as in the First Roman Ordo (sixth to seventh century). In pre-1970 editions of the Roman Missal, the word Introitus was used, distinguished from the normal meaning of the word (entrance) by being capitalized. In Ambrosian chant and Beneventan chant, the counterpart of the Introit is called the "ingressa". In the Mozarabic, Carthusian, Dominican, and Carmelite Rites, it is called the "officium".

Originally, the entrance of the priest who was to celebrate Mass was accompanied by the singing of a whole psalm, with Gloria Patri (doxology). While the psalm was at first sung responsorially, with an antiphon repeated by all at intervals, while a solo singer chanted the words of the psalm, it was soon sung directly by two groups of singers alternating with each other, and with the antiphon sung only at the beginning and the end, as is the usual way of chanting the psalms in the Liturgy of the Hours. The change to this manner of singing the psalm has been attributed to Pope Celestine I (422-432). Pope Gregory I (590-604), after whom Gregorian chant is named, composed several antiphons for singing with the Entrance psalm.

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