In the Constitution Ineffabilis Deus of 8 December, 1854, Pius IX pronounced and defined that the Blessed Virgin Mary "in the first instance of her conception, by a singular privilege and grace granted by God, in view of the merits of Jesus Christ, the Saviour of the human race, was preserved exempt from all stain of original sin."
"The Blessed Virgin Mary..."
The subject of this immunity from original sin is the person of Mary at the moment of the creation of her soul and its infusion into her body.
"...in the first instance of her conception..."
The term conception does not mean the active or generative conception by her parents. Her body was formed in the womb of the mother, and the father had the usual share in its formation. The question does not concern the immaculateness of the generative activity of her parents. Neither does it concern the passive conception absolutely and simply (conceptio seminis carnis, inchoata), which, according to the order of nature, precedes the infusion of the rational soul. The person is truly conceived when the soul is created and infused into the body. Mary was preserved exempt from all stain of original sin at the first moment of her animation, and sanctifying grace was given to her before sin could have taken effect in her soul.
"...was preserved exempt from all stain of original sin..."
The formal active essence of original sin was not removed from her soul, as it is removed from others by baptism; it was excluded, it never was in her soul. Simultaneously with the exclusion of sin. The state of original sanctity, innocence, and justice, as opposed to original sin, was conferred upon her, by which gift every stain and fault, all depraved emotions, passions, and debilities, essentially pertaining to original sin, were excluded. But she was not made exempt from the temporal penalties of Adam — from sorrow, bodily infirmities, and death.
"...by a singular privilege and grace granted by God, in view of the merits of Jesus Christ, the Saviour of the human race."
The immunity from original sin was given to Mary by a singular exemption from a universal law through the same merits of Christ, by which other men are cleansed from sin by baptism. Mary needed the redeeming Saviour to obtain this exemption, and to be delivered from the universal necessity and debt (debitum) of being subject to original sin. The person of Mary, in consequence of her origin from Adam, should have been subject to sin, but, being the new Eve who was to be the mother of the new Adam, she was, by the eternal counsel of God and by the merits of Christ, withdrawn from the general law of original sin. Her redemption was the very masterpiece of Christ's redeeming wisdom. He is a greater redeemer who pays the debt that it may not be incurred than he who pays after it has fallen on the debtor.
Such is the meaning of the term "Immaculate Conception."
Proof from Scripture
No direct or categorical and stringent proof of the dogma can be brought forward from Scripture. But the first scriptural passage which contains the promise of the redemption, mentions also the Mother of the Redeemer. The sentence against the first parents was accompanied by the Earliest Gospel (Proto-evangelium), which put enmity between the serpent and the woman: "and I will put enmity between thee and the woman and her seed; she (he) shall crush thy head and thou shalt lie in wait for her (his) heel" (Genesis 3:15). The translation "she" of the Vulgate is interpretative; it originated after the fourth century, and cannot be defended critically. The conqueror from the seed of the woman, who should crush the serpent's head, is Christ; the woman at enmity with the serpent is Mary. God puts enmity between her and Satan in the same manner and measure, as there is enmity between Christ and the seed of the serpent. Mary was ever to be in that exalted state of soul which the serpent had destroyed in man, i.e. in sanctifying grace. Only the continual union of Mary with grace explains sufficiently the enmity between her and Satan. The Proto-evangelium, therefore, in the original text contains a direct promise of the Redeemer, and in conjunction therewith the manifestation of the masterpiece of His Redemption, the perfect preservation of His virginal Mother from original sin.
Today is a Holy Day of Obligation in the United States, a day on which we celebrate the Immaculate Conception of the Virgin Mary (the Immaculate Conception has been, since 1846, the Patroness of the United States). Note that it is she, Mary herself, who is the Immaculate Conception; the day does not refer to Mary's conceiving Jesus by the Holy Ghost, but to the conception of Mary in the womb of her mother, St. Anne, by Mary's father, St. Joachim. What makes her conception immaculate is not that she was conceived by the Holy Ghost of a virgin, as was Christ Our Lord, but that from the very moment of her conception, she was filled with grace by God, Who knew, in His omniscience, that she would say "yes" to the Angel Gabriel and become the Mother of the Savior. Exactly nine months from now, on September 8, we will celebrate Mary's birthday.
Most of what we know about Mary's parents, SS. Anne and Joachim, is derived from the apocryphal Protoevangelium of St. James and the Gospel of the Nativity of Mary. St. Anne is the patron of childless people, pregnant women, and grandmothers (her Feast Day is 26 July); St. Joachim is the patron of grandfathers. (In the painting above, St. Anne sits in the chair, and her husband stands at her right. Cleophas is seen in the right-hand corner reading, and Jesus, Mary and Joseph are in front).
As said, at the very moment of Mary's conception in St. Anne's womb, God filled Mary with grace and preserved her from the stain of sin so she might be a pure vessel by whom Christ could enter the world; "Immaculate Conception," then is a title for Mary -- a title reflecting her being and which reveals that the New Adam saved the New Eve from the stain of original sin in an act foretold in the first Book of Scripture:
I will put enmities between thee and the woman, and thy seed and her seed: she shall crush thy head, and thou shalt lie in wait for her heel.
Adam and Eve, Mary and Jesus -- the only four persons with human natures who were, in their first moments, without sin (and, of course, Mary and Jesus remained sinless).
Mary is the All Holy, and it had to be this way: Christ took from her His very Flesh and Blood -- the Flesh that was scourged for us, the Blood that was spilt for us, the Bread of Life that saves us!
Symbols for the day are any of the usual Marian symbols (the color blue, her crown of 12 stars representing the 12 Tribes of Israel and the 12 Apostles), but especially those which emphasize her purity, such as lilies and her Immaculate Heart.
There are no special practices today that I know of, but, as with all Marian Feasts, it is a good day to pray the Magnificat, the Litany of Loreto, the Little Crown of the Blessed Virgin, the Akathistos Hymn to the Theotokos, the Ave Maris Stella (Hail, Star of the Ocean), the Glorious Mysteries of the Rosary, etc. (You can download the Litany of Loreto in Microsoft Word .doc format, in English or in Latin.)
The Epistle reading today will be from Proverbs 8:23-25, the Gradual will be Judith 13:23, the Tract will be Psalm 86:1, and the Gospel will be Luke 1:26-28.