Ember Saturday in Advent is a greater ferial day of simple rite and its liturgical colour is violet. The Vigil of St. Thomas the Apostle is commemorated at Mass only. Today is one of the traditional days for ordinations. The feast of St. Thomas is transferred to Monday.
At Mattins the invitatory Prope est jam Dominus etc is sung and the Office hymn is Verbum supernum prodiens. In the nocturn the antiphons and Psalms of Saturday, 97, 98, 99, 100, 101, 102, 103, 104, 105, 106, 107 & 108, are sung. The lessons in the nocturn are taken from a homily of St. Gregory on St. Luke's Gospel. Again, as noted on the other Ember Days, these are significantly longer than the text found in the later editions of the Breviary with most of the text of the third lesson absent from the later books.
At Lauds the antiphons Ecce veniet etc (appointed for the Monday before the Vigil of the Nativity but used today as they are displaced by the feast of St. Thomas the Apostle) are sung with the Psalms of Saturday, 50, 91, 62-66, Audite coeli & 148-149-150. The fourth antiphon from this set, Haurietis aquas etc, is replaced by the antiphon Exspectetur etc which is sung with the Canticle of Moses. The Office hymn is Vox clara . After the antiphon on the Benedictus, Quomodo fiet istud etc, has been sung in full after the NT canticle the choir kneels for the ferial preces which include the Psalm De profundis. The collect is proper to the Ember Saturday, Deus qui conspicis.
At the Hours the antiphons Ecce veniet etc are used in the usual order. At Prime (Pss 53, 118i & 118ii) the chapter is the ferial Pacem et veritatem. The Dominical and ferial preces are sung with the choir kneeling. At the other Hours the short set of ferial preces are sung, again with the choir kneeling.
Mass is sung after None and has the usual, ancient, form, common to Ember Saturdays. The ministers wear folded chasubles. After the Kyrie there are a series of five structural units comprising of the invitation Oremus, followed by Flectamus genua (sung by the deacon), Levate (sung by the sub-deacon), a collect, O.T. reading and gradual. Four of these readings are from Isaiah and the last from Daniel. After the pericope from Daniel instead of a gradual the hymn of the Three Men in fiery furnace is sung, Benedictus es, Domine, Deus patrum nostrorum and its collect Deus, qui tribus pueris. After this collect the second collect is of the Vigil of St. Thomas and the third collect is of the BVM, Deus, qui de Beate. Mass then continues as usual (with of course kneeling for the orations and from the Canon through to the Fraction as usual on penitential days) with Benedicamus Domino, sung as the dismissal by the deacon facing the altar. Ember Saturday ends with the Mass after None.
In the afternoon at Vespers the antiphons and Psalms of Saturday (Pss. 143, 144, 145, 146 & 147) are sung. The Office hymn is Conditor alme siderum. The Great 'O' Antiphon O clavis David is sung entire both before and after the Magnificat, even on days of simple rank, with the choir standing. After the antiphon has been repeated the collect for the fourth Sunday of Advent is sung. At Compline the Dominical preces are sung (the choir standing).