The Immaculate Conception

Many Catholics confuse the doctrine of the Immaculate Conception to refer to the virgin-birth of Christ, however this is incorrect. Rather, this doctrine refers to our Lady being preserved from original sin. The true definition:

The Immaculate Conception is "the doctrine that our Lady, in the first instant of her conception was, by a unique singular grace and privilege of Almighty God in view of the merits of Jesus Christ the Saviour of the human race, preserved exempt from all stain of original sin." (Definition from A Catholic Dictionary, 1951)
 

References in Scripture:

• "One is my dove, my perfect one is but one, she is the only one of her mother, the chosen of her that bore her. The daughters saw her, and declared her most blessed: the queens and concubines, and they praised her. Who is she that cometh forth as the morning rising, fair as the moon, bright as the sun, terrible as an army set in array?" Canticles 6:8-9
• "And the angel being come in, said unto her: Hail, full of grace, the Lord is with thee: blessed art thou among women. Who having heard, was troubled at his saying, and thought with herself what manner of salutation this should be. And the angel said to her: Fear not, Mary, for thou hast found grace with God." Luke 1:28-30

Church Teaching on the Immaculate Conception:

• "And thus, in whatever manner the Blessed Virgin would have been sanctified before animation, she could never have incurred the stain of original sin" St. Thomas Aquinas, Summa Theologica (13th century), Whether the Blessed Virgin was sanctified before animation?
• "This same holy Synod doth nevertheless declare, that it is not its intention to include in this decree, where original sin is treated of, the blessed and immaculate Virgin Mary, the mother of God; but that the constitutions of Pope Sixtus IV., of happy memory, are to be observed, under the pains contained in the said constitutions, which it renews" Council of Trent, Session the Fifth, Decree Concerning Original Sin
• "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." Encyclical On The Immaculate Conception by Pope Pius IX, 1849
• "Moreover, it seems that the Blessed Virgin Mary herself wished to confirm by some special sign the definition, which the Vicar of her Divine Son on earth had pronounced amidst the applause of the whole Church. For indeed four years had not yet elapsed when, in a French town at the foot of the Pyrenees, the Virgin Mother, youthful and benign in appearance, clothed in a shining white garment, covered with a white mantle and girded with a hanging blue cord, showed herself to a simple and innocent girl at the grotto of Massabielle. And to this same girl, earnestly inquiring the name of her with whose vision she was favored, with eyes raised to heaven and sweetly smiling, she replied: "I am the Immaculate Conception." Encyclical On Proclaiming a Marian Year to Commemorate the Centenary of the Definition of the Dogma of the Immaculate Conception, 1953
   

Summary

The Immaculate Conception of the Blessed Virgin Mary shows to have been believed universally since the early centuries of the Catholic Church. So universal and long standing has this teaching been in the Catholic Church, that it was defined as a Catholic Dogma in 1849 through the solemn magisterium of the Church. Those who do not believe in this dogma cannot call themselves Catholic!