It means that you say the entire Office proscribed for December 17th - 31st. No considerations are made for saints beyond what is written in the texts for those specific days. Generally substitutions are made in the Office throughout the year if it is a saint’s day. During Tempus per Annum (i.e.: for Americans, “Ordinary Time”) when Saint X’s Day arrives one replaces, for instance, the generic Benedictus antiphon of Monday Week II Morning Prayer with the antiphon from whatever Commons the saint belongs to. If the saint is especially important he will have a special antiphon which even replaces the one in the Commons. During Advent and Christmas this system works differently because they are considered a “privileged seasons.” Even within this special time, there is “special-er” time. These are the days of December 17th - 31st. As a way to acknowledge this the Office allows for considerations to be made of saints, but only in a limited way. The outstanding exceptions to this are the feasts of Ss. Stephen, Jo. and the Holy Innocents. For less important saints like Tho. Becket or Jo. of Kanty, we - with them - keep our eyes fixed solely on the events of the Incarnation. Should you want to remember those men on their feast days you may sing their Gospel Canticle from the correct Common or Proper following the closing Collect but before the recitation of the day’s
Martyrology and closing blessing
ad libitum (i.e.: freely, at your discretion). You would also say their special prayer immediately after the saint’s antiphon. This is similar to what happens during Lent.
For the upcoming feast of Tho. Becket Morning Prayer would look like this if you choose to remember him in the Office:
- [Everything from the Morning Prayer of the Fifth Day in the Octave of Christmas, closing Collect inclusive] “…We ask this through our Lord Jesus Christ… Amen,”
- [Antiphon of S. Tho.] “Whoever hates his life in this world keeps it safe for life everlasting,”
- [Collect of S. Tho.] “Almighty God, you granted the martyr Thomas…,”
- [If you choose to recite it] Martyrology selection for 29th of December,
- [Closing blessing] If cleric present: “The Lord be with you… Amen,” amongst laymen or in private for clergy: “May the Lord bless us, protest us from all evil…Amen.”