On this and the following eight days the Church celebrates, with particular solemnity, the immaculate conception of the ever-blessed Virgin Mary, who, from all eternity, was chosen to be the daughter of the heavenly Father, the spouse of the Holy Ghost, the Mother of the divine Redeemer, and, by consequence, the queen of angels and of men. The consideration of these prerogatives convinced the most enlightened fathers and teachers of the Catholic Church that she was conceived immaculate, that is, without original sin. It is very remarkable that among the shining hosts of saints who have, in every century, adorned the Church no one wrote against this belief, while we find it confirmed by the decisions of the holy fathers from the earliest times. Pope Pius IX, forced, as it were, by the faith and devotion of the faithful throughout the world, finally, on 8 December 1854, sanctioned, as a dogma of faith falling within the infallible rule of Catholic traditions, this admirable prerogative of the Blessed Virgin. It is, therefore, now no longer, as fomerly, a pious belief, but an article of the faith, that Mary, like the purest morning light which precedes the rising of the most brilliant sun, was, from the first instant of her conception, free from original sin.
In the Introit of the Mass the Church sings: "I will greatly rejoice in the Lord, and my soul shall be joyful in my God; for He hath clothed me with the garments of salvation, and with the robe of justice He hath covered me, as a bride adorned with her jewels. I will extol thee, O Lord, for Thou hast upheld me: and hast not made my enemies to rejoice over me." Glory be to the Father, and to the Son, and to the Holy Spirit. As it was in the beginning, is now, and forever shall be, world without end. Amen.
We beseech Thee, O Lord, to bestow on Thy servants the gift of heavenly grace, that, for those to whom the Blessed Virgin's maternity was the beginning of salvation, the votive solemnity of her immaculate conception may procure increase of peace. Through Christ our Lord, etc. Amen.
Epistle: Proverbs 8:22-35
The Lord possessed Me in the beginning of His ways, before He made anything from the beginning. I was set up from eternity, and of old before the earth was made. The depths were not as yet, and I was already conceived, neither had the fountains of waters as yet sprung out: the mountains with their huge bulk had not as yet been established: before the hills I was brought forth: He had not yet made the earth, nor the rivers, nor the poles of the world. When He prepared the heavens, I was present: when with a certain law and compass He enclosed the depths: when He established the sky above, and poised the fountains of waters: when He compassed the sea with its bounds, and set a law to the waters that they should not pass their limits: when He balanced the foundations of the earth, I was with Him forming all things; and was delighted every day, playing before Him at all times; playing in the world, and My delights were to be with the children of men. Now, therefore, ye children, hear Me: Blessed are they that keep My ways. Hear instruction and be wise, and refuse it not. Blessed is the man that heareth Me, and that watcheth daily at My gates, and waiteth at the posts of My doors. He that shall find Me shall find life, and shall have salvation from the Lord.
This lesson is, in the literal sense, a eulogy on the divine and uncreated wisdom, which before all things was in God; through which all things were made, disposed, and preserved; which rejoices in its works, and calls upon all its creatures, especially on men, to render to it love and obedience. Most of what is here said is also to be applied to Mary, of whom it may with truth be said that, as the holiest and most admirable of all creatures, she occupies the first place in the heart of God. Therefore the Church also refers to her those words of the wise man: "I came out of the mouth of the Most High, the first born of all creatures."
Gospel: Luke 1:26-28
And in the sixth month the angel Gabriel was sent from God into a city of Galilee, called Nazareth, to a virgin espoused to a man whose name was Joseph, of the house of David, and the virgin's name was Mary. And the angel being come in, said unto her: Hail, full of grace; the Lord is with thee; blessed art thou among women.
--Goffine's Devout Instructions