Saturday of Ember Week in Advent
For the church in Rome in the early centuries, Saturday was the most solemn of the Ember Days, because that was the day on which the Church ordained her priests in the great Basilica of St Peter's. The ordination in the tenth month of the year (called for that reason December) was the only one originally known at Rome. Hence it was an important date.
Everything in the Mass, moreover, bears the character of a very ancient liturgy. It calls to mind, with its numerous lessons, intermingled with responses and prayers, the earliest form of the introductory part of the Mass.
The soul that is penetrated with it finds itself filled with a holy impatience, and with the church it aspires to the new birth of the only begotten son of God, who comes to deliver us from the yoke of sin (second collect). "While with confidence she awaits the Lord Jesus Who shall deliver us from our enemies, destroying Antichrist with the brightness of His coming" (Epistle).
The Gospel brings before us the image of St John the Baptist the precursor, who prepares our souls each year for the coming of the Saviour. The same Gospel is again found in the Mass of the following day, because formerly the ordination, taking place in the evening, lasted well into the night thus encroaching on the Sunday, provided it with its liturgy.