It’s logical to conclude that the Immaculate Conception refers to Christ because the Gospel at the Dec. 8 Solemnity Mass is about our Lord’s conception.
But the title and the feast day belong to the Blessed Virgin Mary. Her conception isn’t explicitly mentioned in the bible, so it’s also logical to ask on what basis the Church teaches that her conception was immaculate.
Probably the strongest argument for Mary’s Immaculate Conception is that not just anybody could become the mother of God without a lot of grace.
The Vatican II document Lumen Gentium teaches that the Blessed Virgin:
“gave the world the Life that renews all things, and who was enriched by God with gifts appropriate to such a role. It is no wonder then that it was customary for the Fathers to refer to the Mother of God as all holy and free from every stain of sin, as though fashioned by the Holy Spirit and formed as a new creature.” (LG 56)
In 1854, the long-held Church belief in the Blessed Mother’s Immaculate Conception became Church dogma with foundation in scripture and tradition. 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 Serpent’s Enemy
The first bible passage mentioning the promise of redemption also mentions the Mother of the Redeemer. After the Fall, God told the serpent, “I will put enmity between you and the woman and between your offspring and hers; He will strike at your head, while you strike at his heel.” (Gen. 3:15)
Jesus is the conqueror who comes from the woman’s seed and who crushes the serpent’s head while Mary is the woman who is the enemy of the serpent. Mary’s continual union with grace explains the enmity between her and Satan.
Given from her conception “the splendor of an entirely unique holiness,” the Blessed Virgin is hailed by the Angel Gabriel in Luke 1:28 as “full of grace” (LG 56) The angel’s term (kechairitomene in Greek) is not applied to any other person in scripture. According to Pope Pius, that “showed that the Mother of God is the seat of all divine graces and is adorned with all gifts of the Holy Spirit.”
Through the millenia, Church fathers and theologians have studied the issue of Our Lady’s conception. All insist on her absolute purity and her position as the second Eve. (I Cor. 15:22)
In the fourth century, St Ephraem asserted that Mary was as innocent as Eve before the Falll, a virgin without any stain of sin, holier than the seraphim, the sealed fountain of the Holy Spirit, and the pure seed of God. In mind and body she always was intact and immaculate. During the following century, Maximus of Turin called the Blessed Mother a dwelling fit for Christ, not because of her habit of body, but because of original grace.
In her own words
Another reason to believe Mary is the Immaculate Conception is that she herself has said so more than once in the last couple hundred years.
In 1830 the Blessed Virgin appeared to a French nun named Catherine Laboure and told her to place this prayer on what would become the Miraculous Medal: “O Mary, conceived without sin, pray for us who have recourse to thee.” Then in 1858, only a few years after Pope Pius IX’s proclamation, she appeared to a young girl named Bernadette Soubirous in Lourdes, France, and told her, “I am the Immaculate Conception.”
Apparitions don’t fit well into a logical argument, but the idea that God provides what we need for the tasks He gives us makes sense. Giving birth to the Savior and raising Him were not small assignments.