The feast of the Nativity of the LORD is a double of the first class with a privileged octave of the third order.
Mattins is sung late in the evening, so that the Mass which immediately follows can begin at midnight. The Caeremoniale gives special instructions, Lib.II, Cap. XIV, 3, for Pontifical Mattins, but may be reasonably applied to other celebrations or arranging adequate candles to supply light for the service and talks of candelabris ferreis magnis to help provide this. One can easily see the modern practice of candlelit nine lessons and carols comes from - how unfortunate that the same effort is not made to celebrate solemn Mattins.
The invitatory is proper, Christus natus es nobis: Venite adoremus. When intoning the hymn, Jesu, Redemptor omnium, the Hebdomadarius turns and bows to the altar. Mattins has three nocturns and the usual nine lessons. In the first nocturn the lessons are from Isaiah but, interestingly, are sung without a title. In the second nocturn the lessons are taken from a homily on the Nativity by St. Leo. In the third nocturn three Gospel pericopes are sung, two from St. Luke and the third from St. John. After the Te Deum the collect is sung followed by Benedicamus Domino. Then first of the three Masses for the Nativity is then sung. The Gloria is sung (one theory of its origin in the Mass rite is from the song of the Angels on Christmas night to the shepherds) as is the Creed. The preface and communicantes are of the Nativity. Lauds, with different antiphons to those used at first vespers, immediately follows this Mass.
Later in the morning Prime is sung. All hymns of Iambic metre have the tone and Doxology in honour of the Incarnation, Jesu tibi sit gloria etc. The first antiphon from Lauds is sung with the festal psalms. In the short responsory the versicle Qui natus es de Maria Virgine is sung . Prime is followed by the second Mass, the Missa in aurora, that has a second collect to commemorate St. Anastasia. The Gloria and Creed are sung, the preface and communicantes are of the Nativity.
After Terce the third Mass is sung. This Mass too has the Gloria and Creed along with the preface and communicantes of the Nativity. As the Gospel pericope for this Mass is In principio the Gospel of the Epiphany is read as a proper last Gospel.
Second Vespers has yet a third set of proper antiphons for the feast and will be used through the Octave. The following feast of St. Stephen is commemorated.
In the 'liturgical books of 1962' at Mattins, and for the Octave, psalm 88, Misericordias Domini is cut from 51 to 36 verses. The verses from Tu vero repulisti et despexisti to the end are omitted. The tone and Doxology in honour of the Nativity is not sung at the hymns of the Little Hours. In the third Mass the last Gospel is omitted and at Vespers no commemoration of St. Stephen is made.
May all readers have a very blessed and Holy Christmas