At Vespers on these days, we pray one of the "O" antiphons at the Magnificat. Today, December 19, the antiphon is "O radix Iesse":
O radix Iesse qui stas in signum populórum, super quem continebunt reges os suum, quem Gentes deprecabúntur: veni ad liberándum nos, iam noli tardare.
O Root of Jesse, who stands as an ensign to the peoples; because of whom kings shall shut their mouths; whom the nations shall seek; come and free us, do not any longer delay!
From "Liturgical Meditations for the Entire Year" by the Sisters of St. Dominic, Adrian, MI (B. Herder, 1960):
Today's liturgy takes us back more than ten centuries before the birth of Christ to the Bethlehem shepherd, Jesse, and his son, David the king. Called by God's prophet from his father's flocks to the throne of Israel, David was the head of the royal family glorified by the human ancestry of Christ. Many weary decades of humiliation and obscurity were to visit the descendants of Jesse before the pre-eminent Son of David would come to save His people.
In the vicissitudes of the Hebrew family from whom Christ derived His human origin, we may see a figure of our spiritual lives. Anointed to the royal priesthood of Christ by the charism of baptism, we must endure suffering and humiliation before His image appears in us. Purified by trial and chastened by mortification, we shall in God's time yield the fruits of sanctification unto eternal life.