“We declare, pronounce, and define that the doctrine which holds that the most Blessed Virgin Mary, in the first instance of her conception, by a singular grace and privilege granted by Almighty God, in view of the merits of Jesus Christ, the Saviour of the human race, was preserved free from all stain of original sin, is a doctrine revealed by God and therefore to be believed firmly and constantly by all the faithful.”
(Pope Pius IX, Ineffabilis Deus, 8 December 1854)
The month of December is traditionally dedicated to the Immaculate Conception. The Solemnity is a Holy Day of Obligation and falls on 8th December (Mass times). For many centuries the Church acknowledged the Immaculate Conception of the Virgin Mary. In 1477 Pope Sixtus IV approved a Mass and Office for the feast. In 1693 Pope Innocent XII proclaimed that the feast be universally celebrated.
However, it wasn’t until 8th December 1854 that the doctrine of the Immmaculate Conception was defined ex cathedra in the Apostolic Constitution Ineffabilis Deus of Blessed Pope Pius IX. By this action the Holy Father infallibly taught that the Blessed Virgin Mary was conceived in her mother’s womb with the stain of Original Sin excluded from her soul. The Angel Gabriel addressed Mary as being one “full of grace” (Lk 1: 31-33). Her Immaculate Conception was a gratuitous favour from God for the one chosen to be the Mother of His Divine Son. From the beginning of her life Mary was endowed with all the perfections and graces that befitted her role as mother of the Saviour.
At the beginning of December the Church passes from the period of Ordinary Time to the liturgical season of Advent. It is a time of preparation for the Church as it readies itself to commemorate the birth of the Redeemer. It is fitting that the Feast of the Immaculate Conception is celebrated during this season for it recalls how God suitably prepared Mary to become the Mother of the Word Incarnate.
Resources
Immaculate Conception Defined by Pius IX
Catechesis offered by Pope John Paul II at a General Audience
Novena to the Immaculate Conception
Nine days of prayer in preparation for the Feast on 8th December