Beginning today, we enter a more profound period in the Advent Season. The days from December 17 to December 23 are the Advent equivalent of Passiontide in Lent. During this time, the ferial days are II Class, and take precedence over III Class feast of saints (a commemoration is made during this time, of any III Class feast in the Proper of the Saints).
At Vespers on these days, we pray one of the "O" antiphons at the Magnificat. Today, December 17, the antiphon is "O Wisdom":
O Sapiéntia quæ ex ore Altíssimi prodiisti, attingens a fine usque ad finem, fórtiter suaviterque disponens ómnia: veni ad docendum nos viam prudéntiæ.
O Wisdom, who came forth from the mouth of the Most High, and reaches mightily from one end of the earth to the other, ordering all things well’ come and teach us the way of understanding.
From "Liturgical Meditations for the Entire Year" by the Sisters of St. Dominic, Adrian, MI (B. Herder, 1960):
Holy Mother Church begins today her immediate preparation for Christmas by contemplating the divine and eternal origin of Him who is to come. From all eternity the only-begotten Son of God, eternal uncreated Wisdom, came forth from the depths of the divine Mind, the perfect image of the Father’s splendor, “the brightness of His glory and the figure of His substance.” (Heb. 1.3) From all eternity He willed to become man in order to redeem us from our sins and to show us in human form the infinite goodness, truth, and beauty of God.
In eternal silence the Word proceeded from the divine Intellect and in profound silence He assumed our nature in the womb of the immaculate Virgin. In silence the divine Word comes to our souls with His generous gifts and loving inspirations. I n the tranquility of recollection and the profound peace of a silent soul we must receive Him who comes to us. Let us never permit our duties to hinder our recollection and disturb our preparation for the coming of our divine Lord. None of these external affairs can penetrate the sanctuary of our souls unless we allow them to do so by anxiety about the success of our endeavors or preoccupation with matters of small import for eternity.