What is the Immaculate Conception, then? Well, finding that the definition of an earlier Pope on the subject was the best expression of the Church's teaching and understanding, Pope Pius IX declared in Ineffabilis Deus, published on the feast in 1854:
We declare, pronounce and define that the doctrine which holds that the Blessed Virgin Mary, at the first instant of her conception, by a singular privilege and grace of the Omnipotent God, in virtue of the merits of Jesus Christ, the Saviour of mankind, was preserved immaculate from all stain of original sin, has been revealed by God, and therefore should firmly and constantly be believed by all the faithful.The Church has always believed Mary's conception was special in some way and that her fullness of grace stemmed from this. This can be seen from the number of places (the United States after the Plenary Council of Baltimore in 1846!) and organizations placed under the patronage of this title, as well as the liturgical celebrations.
When devotion to Our Lady of Lourdes spread, so did devotion to her Immaculate Conception, for the Blessed Mother introduced herself to St. Bernadette by saying, "I am the Immaculate Conception." This is also fascinating since devotion to her Immaculate Heart spread with the promulgation of the Miraculous Medal in the early 19th century, also in France...
So interesting that she is the Immaculate Conception. St. Maximilian Kolbe dedicated his life to pondering the question of who is the Immaculate Conception, and in his final hours prior to his arrest by the Gestapo on February 17, 1941 wrote a brief sketch of this answer. The Immaculate Conception is relational, just as Love is relational.
If among human beings the wife takes the name of her husband because she belongs to him, is one with him, becomes equal to him and is, with him, the source of new life, with how much greater reason should the name of the Holy Spirit, who is the divine Immaculate Conception, be used as the name of her in whom he lives as uncreated Love, the principle of life in the whole supernatural order of grace?Finally, I would like to share today's Introit (tomorrow's I suppose in the Novus Ordo). It is sublime.