What is the Immaculate Conception?
The solemnity of the Immaculate Conception is a celebration of the dogma in the Church that states that the Virgin Mary was conceived without the stain of original sin. This dogma was defined after a long process of discernment in the Church, in which the “sensum fidelium” (sense of the faithful) played a very important role.
The belief that Mary was “preserved free from all stain of original sin” from the moment of her conception was a popular belief for centuries in the Church, and the celebration of this doctrine on Dec. 8 continues to be an important feast for Catholics around the world. 
On Dec. 8, 1854, Pope Pius IX (Giovanni Maria Mastai Ferretti, 1792-1878) proclaimed with the papal bull “Ineffabilis Deus” the dogma of the Immaculate Conception of the Virgin Mary. The text states: “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 Savior 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.”
The Catechism of the Catholic Church summarizes the teaching of the Immaculate Conception in this way: “God sent forth his Son, but to prepare a body for him, he wanted the free co-operation of a creature. For this, from all eternity God chose for the mother of his Son a daughter of Israel, a young Jewish woman of Nazareth in Galilee, ‘a virgin betrothed to a man whose name was Joseph, of the house of David; and the virgin's name was Mary’: The Father of mercies willed that the Incarnation should be preceded by assent on the part of the predestined mother, so that just as a woman had a share in the coming of death, so also should a woman contribute to the coming of life” (No. 488).
Reflecting on the “mystery of the Immaculate Conception,” Benedict XVI called it a “source of inner light, hope and comfort" during his Angelus address on Dec. 8, 2010.
In his 2009 pilgrimage to the figure of the Immaculate Conception at the Spanish Steps (a plaza in Rome), the Pontiff added that “Mary Immaculate helps us to rediscover and defend what lies within people, for in her is a perfect transparency of the soul in the body. She is purity in person, in the sense that spirit, soul and body are fully consistent with one another and with God's will.”
That same day, before praying the Angelus with those gathered in St. Peter’s Square, the Pope invited the faithful to approach Mary as they would their own mother: “Every time we experience our frailty and the promptings of evil, we may turn to her and our hearts receive light and comfort.”
In the case of the Immaculate Conception, the devotion of the faithful had preceeded the formulation of the dogma, which can be traced back to the first centuries of the Church. In the Middle Ages, a controversy arose surrounding the doctrine that reached epic proportions. In the 11th century, for example, the feast had been abolished in England by Norman invadors, and as the controversy continued into the 15th century, university professors and students made blood pacts to defend the doctrine of the Immaculate.
When the dogma of the Immaculate Conception was defined in 1854, the news was received with great celebrations. Within just a few decades, the feast acquired the character of solemnity on par with the other great feasts of the Christian calendar.
The Immaculate Conception was declared Patroness of the United States in 1847. In Spain, the first known celebration of the feast dates back to as far back as the eighth century, and since 1864, the priests of Spain have been given the pontifical priviledge of celebrating the solemnity of the Immaculate Conception using a blue chasuble. In Rome, the reigning pope visits the Spanish Steps in Rome to pay homage to the plaza’s image of the Immaculate Virgin on her feast day. The feast is also celebrated with great solemnity and devotion, with great feasts and processions, in Argentina, Panama, Colombia, Peru, Ecuador, Chile, Guatemala, Mexico, Nicaragua and Brazil.
Many saints have spoken fondly of the Immaculate. One of them was, for example, St. Maximilian Kolbe, who said that "The Holy Spirit dwells in her, lives in her. This was true from the first instant of her existence. It was always true; it will always be true."
As John Paul II wrote in his encyclical letter “Redemptoris Mater”: “The Mother of God is already the eschatological fulfillment of the Church. [...] The pilgrimage of faith no longer belongs to the Mother of the Son of God: glorified at the side of her Son in heaven, Mary has already crossed the threshold between faith and that vision which is ‘face to face.’ At the same time, however, in this eschatological fulfillment, Mary does not cease to be the ‘Star of the Sea’ (Maris Stella) for all those who are still on the journey of faith.”
The papal definition of Mary's immaculate conception as dogma concluded a centuries-long journey of theological and doctrinal discernment in the Church. 
Pius IX’s decision in 1854 to define the doctrine of the Immaculate Conception as a dogma was the culmination of a long tradition of devotion to Mary Immaculate. From the first centuries of Christianity, and especially in the East, the Church had celebrated Mary's purity. St. Ephraem the Syrian (d. 373) wrote that Mary was “most holy, all-pure, all-immaculate, all-stainless, all-undefiled, all-incorrupt, all-inviolate.”
In the West, Church tradition always maintained the doctrine of the Immaculate Conception, but the development of the dogma was linked to theological discernment on the question of Original Sin. The difficulties, debated mostly in Europe in the 12th century, followed two lines: in the first place, if Mary was an exception (if she wasn't affected by Original Sin), then she did not need to be redeemed, and then redemption couldn’t be considered universal, which would contradict St. Paul. In the second place, there was discussion about the moment in which Mary had remained free from sin -- whether before or immediately after her conception -- because there wasn’t agreement about the way in which Original Sin was transmitted.
Even theologians such as St. Bernard of Clairvaux and St. Thomas Aquinas objected to the doctrine of the Immaculate Conception. After decades of debate, however, the Franciscan John Duns (1265-1308), known as Duns Scotus because of his Scottish origin, laid the foundations for the true doctrine “so solidly and dispelled the objections in a manner so satisfactory, that from that time onward the doctrine prevailed,” comments the Catholic Encyclopedia.
Benedict XVI, in his Wednesday catechesis on July 7, 2010, reflected on the contribution of the Franciscan in the debate on the Immaculate Conception, noting that “the majority of theologians countered with an objection that seemed insurmountable, the doctrine which holds that Mary Most Holy was exempt from original sin from the very first moment of her conception: in fact, at first sight the universality of the Redemption brought about by Christ might seem to be jeopardized by such a statement, as though Mary had had no need of Christ or his redemption. Therefore the theologians opposed this thesis.”
“Thus,” the Pope continued, “to enable people to understand this preservation from original sin Duns Scotus developed an argument that was later, in 1854, also to be used by Blessed Pope Pius IX when he solemnly defined the Dogma of the Immaculate Conception of Mary. And this argument is that of ‘preventative [anticipatory] redemption,’ according to which the Immaculate Conception is the masterpiece of the Redemption brought about by Christ because the very power of his love and his mediation obtained that the Mother be preserved from original sin. Therefore Mary is totally redeemed by Christ, but already before her conception. Duns Scotus' confreres, the Franciscans, accepted and spread this doctrine enthusiastically and other theologians, often with a solemn oath, strove to defend and perfect it.”
Although the work of Scotus was able to sway the opinion of religious and scholars throughout Europe in favor of the doctrine of the Immaculate Conception, and even though the celebration of the feast spread widely, the controversy continued. In 1439, the dispute was taken before the Council of Basle, and after two years of discussion, the bishops declared the Immaculate Conception a pious doctrine in conformity with Catholic worship and faith, right reason, and sacred Scripture, establishing that from that moment onward, it was not permitted to preach or make declarations to the contrary. Nevertheless, since this was not an ecumenical council, its pronouncement did not carry maximum authority.
In 1476, under Pope Sixtus IV, the feast of Mary's Conception was placed on the Roman calendar. In the 16th century, the great universities became bulwarks in defense of the dogma. One who would not vow to do all in his power to defend the Immaculate Conception was not admitted as a member in many universities, including Bologna, Naples, Paris, Cologne, Vienna, Coimbra, Louvain, Salamanca, Seville, Valencia, and (before the English Reformation) Oxford and Cambridge. There were also religious orders dedicated to defending the doctrine, such as the Friars Minor, who in 1621 took the Immaculate Conception as their patron, committing themselves to spreading the doctrine in public and in private.
On Dec. 8, 1661, Pope Alexander VII promulgated the constitution “Sollicitudo Omnium Ecclesiarum,” declaring as an object of faith Mary's immunity from Original Sin from the first moment of the creation of her soul and its infusion in her body. The catechisms of Peter Canisius (1521-1597) and Robert Bellarmine (1542-1621) and Jacques-Bénigne Bossuet (1627-1704), also affirm this.
In 1830, St. Catherine Labouré (1806-1876) saw an apparition of the Virgin, who entrusted to her the task of spreading the "Miraculous Medal" throughout the world. The medal has the image of Mary with the inscription "Conceived Without Sin." The devotion that sprang forth among the faithful was so widespread that many bishops asked Pope Gregory XVI to define the dogma of the Immaculate Conception.
The petitions continued with his successor, Pius IX, who established a special commission of cardinals and members of the secular and religious clergy to carefully examine everything related to the issue. The Pontiff also sent every Catholic bishop the 1849 encyclical “Ubi Primum,” asking that they report on the status of devotion to the Immaculate Conception in their dioceses, and above all, to ask their own opinions on the matter.
In “Ineffabilis Deus” (art 17), Pius IX wrote: “We were certainly filled with the greatest consolation when the replies of our venerable brethren came to us. For, replying to us with a most enthusiastic joy, exultation and zeal, they not only again confirmed their own singular piety toward the Immaculate Conception of the most Blessed Virgin, and that of the secular and religious clergy and of the faithful, but with one voice they even entreated us to define our supreme judgment and authority the Immaculate Conception of the Virgin.”
Four years after the proclamation of the dogma, in 1858, the Virgin appeared in Lourdes, France, to the young Bernadette Soubirous, saying, "I am the Immaculate Conception," thereby confirming Pius IX's proclamation.
Team Aleteia
Benedict XVI made the traditional visit to Piazza di Spagna for today's Feast of the Immaculate Conception where he blessed a basket of roses that was later placed at the feet of the Column of the Immaculate.
