This year, during the season of Advent, we will pray the ferial office 13 time. In the Dominican Breviary, the ferial office in Advent draws heavily from the Book of Jeremiah for the Little Chapter (Lauds, Terce, Sext, and Vespers). The versicle before Lauds is from Isiah 6. Each one builds upon the Old Testament Prophets' anticipation of the coming of the Messiah, just as the Church now does during Advent.
The ferial days in Advent is III Class, until December 17. During these days, when a III Class feast is celebrated, a commemoration is made of the ferial day at Lauds and Vespers. From December 17 through December 23, the ferial days are II Class. During this period, when a III Class feast occurs, the ferial office is prayed and a commemoration of the III Class feast is made at Lauds and Vespers.