Mangenot in Dict. de théol, cath., I, 605; Henry in Dict. d'archéol. I, 909; Kraus, Real-Encyclopädie, I, 29; Barbier de Montault in Analecta Juris Pontificii, VIII, 1475; Baldassari, I Pontifici Agnus Dei (Venice, 1714); Thurston, Holy Year of Jubilee (London, 1900), 247–256; Barbier de Montault, Un Agnus Dei de Grégoire II (Poitiers, 1880); Cozza Luzzi, Sopra un antico atampo di Agnus Dei in the Römische Quartalschrift (1893), 263.
Agnus Dei (In Liturgy), a name given to the formula recited thrice by the priest at Mass (except on Good Friday and Holy Saturday) in the Roman rite. It occurs towards the end of the Canon, after the prayer "Hæc commixtio", etc. Having finished saying this prayer, the priest covers the chalice with the pall, genuflects, rises, inclines his head (but not his body) profoundly towards the altar and, with hands joined before his breast (and not, therefore, resting on the altar), says with a loud voice: "Agnus Dei, qui tollis peccata mundi, miserere nobis" (Lamb of God, Who takest away the sins of the world, have mercy on us), repeats the formula unchanged, and still a third time, substituting now "dona nobis pacem" (grant us peace) for "miserere nobis", meanwhile striking his breast thrice, once at each "miserere nobis" and once at "dona nobis pacem", with the right hand (the left hand resting throughout, from the first "miserere", on the altar). In Requiem Masses, however, the formula occurs at the same part of the rite, but with the substitution of "dona eis requiem" (grant them rest) for "miserere nobis", and of "dona eis requiem sempiternam" (grant them eternal rest) for "dona nobis pacem." In this case, the priest does not strike his breast, but keeps his hands joined before his breast throughout the whole formula. These rubrical details are given here for the reason that both the formula and the ceremonial accompanying it have undergone various changes in different ages and different places. Into the symbolic reasons for the present practice it is not necessary to enter here.
Slightly changed in respect of one word, peccata for peccatum (peccatum, however, appearing in other sources, such as the Missal of Stowe and other English MSS., and in the Bangor Antiphonary), the formula appears to have been directly taken from the very ancient chant of the "Gloria in excelsis." In the text of the Roman and Ambrosian rites: "Agnus Dei, Filius Patris, Qui tollis peccata mundi, miserere nobis; Qui tollis peccata mundi, suscipe deprecationem nostram; Qui sedes ad dexteram Patris, miserere nobis", containing all the words of the original formula of the Agnus Dei, we may find the immediate source of its text. Its remoter source was the declaration of the Baptist: "Ecce Agnus Dei, ecce Qui tollit peccatum mundi" (John, i, 29), supplemented by the cry of the two blind men (Matt. ix, 27): "Miserere nostri, fili David." The scriptural origin of the formula is therefore evident at a glance. Its symbolism, however, is traced in the Apocalypse through the more than thirty references to "the Lamb that was slain from the beginning of the world" (xiii, 8); "the blood of the Lamb" (xii, ii); "they that are written in the book of life of the Lamb" (xxi, 27); and in the following: v, 6, 8, 12, 13; vi, 1, 16; vii, 9, 10, 14, 17; xiv, 1, 4, 10; xv 3; xvii, 14; xix, 7, 9; xxi, 9, 14, 22, 23, 27; xxii, 1, 3, 14. From the Apocalypse we trace it backward to the First Epistle of St. Peter (i, 19): "the precious blood of Christ, as of a lamb unspotted and undefiled"; to the perplexed reading of the eunuch of Queen Candace (Acts, viii, 32, 33): "He was led as a sheep to the slaughter; and like a lamb without voice before his shearer, so openeth he not his mouth…;" and thus finally to the great Messianic chapter of Isaias (liii, 7–12), which formed the subject of the eunuch's query: "I beseech thee, of whom doth the prophet speak this? of himself, or of some other man? Then Philip, opening his mouth and beginning at this scripture, preached unto him Jesus" (Acts, viii, 34, 35). While Isaias compared Our Saviour to a lamb, the Baptist was the first actually to bestow this name upon Our Lord ("Behold the Lamb of God"), and doubtless with a determinate sense derived from ancient type and prophecy. The Christian mind will recall such instances in the Old Testament as the Paschal Lamb of the Jews, "without blemish, a male, of one year" (Exod., xii, 5), whose blood, sprinkled on the door-posts, should save from the Destroying Angel—a figure of the Immaculate Lamb whose blood was to conquer death and to open to men the true Land of Promise; and also the perpetual offering of a lamb morning and night (Exod., xxix, 38, 39)—a figure of the perpetual sacrifice of the altar in the New Dispensation. To the ideas of immaculate purity, gentleness, atoning, and eucharistic sacrifice, the Baptist adds that of universality of purpose: "Who taketh away the sins of the world", and not alone of Israel. From the Baptist the other John caught the fullness of the symbolism and repeated it in the fourth and fifth chapters of the Apocalypse in such a way as to foreshadow the splendours of the Solemn Mass—the Lamb upon the altar as upon a throne; the attendant clergy as four-and-twenty ancients seated, clothed in white vestments; the chanting of the "Sanctus, sanctus, sanctus"; the incense arising from golden censers, and the music of harps; and then, as by a sudden change, in the midst of all "a Lamb standing as it were slain" (v, 6). Naturally, the symbolism of types and figures of the Old Testament, the Messianic prophecy of Isaias, the declaration of the Baptist, the mystical revelations of the Apocalypse, were early commemorated in the morning hymn of the "Gloria in excelsis", which was originally a part of the office of Matins. In a slightly different form it is found in the "Apostolic Constitutions" and in the appendixes to the Bible in the "Codex Alexandrinus" of the fifth century. It first appears in use at Rome, appropriately, in the first Mass of the Nativity. Pope St. Symmachus (498–514) extended its use in episcopal Masses. The distinct and condensed formula of the Agnus Dei itself, however, was not apparently introduced into the Mass until the year 687, when Pope Sergius I decreed that during the fraction of the Host both clergy and people should sing the Agnus Dei: "Hic statuit ut tempore confractionis dominici corporis Agnus Dei, qui tollis peccata mundi, miserere nobis, a clero et a populo decantetur" (Liber Pontificalis, ed. Duchesne, I, 381, note 42). Duchesne, accepting the view of Sergius's reason propounded by Cardinal Bona, says: "il n'est pas defendu de voir, dans ce décret de Sergius, une protestation contre le canon 82 du concile in Trullo, qui proscrivit la representation symbolique du Sauveur sous forme d'agneau".
In the Liturgy of St. James, the priest when signing the Bread, shortly before communicating himself, says: "Behold the Lamb of God, the Son of the Father, who taketh away the sin of the world, sacrificed for the life and salvation of the world." The formula is thus said but once. At about the same part of the Mass in the present Liturgy of St. John Chrysostom, the priest divides the Holy Bread into four parts, "with care and reverence" (in the language of the rubric) and says: "The Lamb of God is broken and distributed; He that is broken and not divided in sunder; ever eaten and never consumed, but sanctifying the communicants" (Neale, History of the Holy Eastern Church, Introduction, 650). These words are absent, however, from the ancient Mass of the Saint (ninth century). In the Office of Prothesis (a sort of preparatory Mass, dealing with the preparation of the "Holy Bread", or "Holy Lamb", as it is called) now in use, the prophecy of Isaias is more minutely referred to in the