Saturday the Catholic Church celebrated the Immaculate Conception of the Blessed Virgin Mary. It is a holy day of obligation on December 8th every year. In 1854, Pope 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."From New Advent
A lot of people may be confused as to what we are celebrating. Every year I would go to mass on this day, but a lot of times not fully aware of what is being celebrated. Below is from catholic.com and explains it all very clearly :)
The Immaculate Conception
It’s important to understand what the doctrine of the Immaculate Conception is and what it is not. Some people think the term refers to Christ’s conception in Mary’s womb without the intervention of a human father; but that is the Virgin Birth. Others think the Immaculate Conception means Mary was conceived "by the power of the Holy Spirit," in the way Jesus was, but that, too, is incorrect. The Immaculate Conception means that Mary, whose conception was brought about the normal way, was conceived without original sin or its stain—that’s what "immaculate" means: without stain. The essence of original sin consists in the deprivation of sanctifying grace, and its stain is a corrupt nature. Mary was preserved from these defects by God’s grace; from the first instant of her existence she was in the state of sanctifying grace and was free from the corrupt nature original sin brings.
When discussing the Immaculate Conception, an implicit reference may be found in the angel’s greeting to Mary. The angel Gabriel said, "Hail, full of grace, the Lord is with you" (Luke 1:28). The phrase "full of grace" is a translation of the Greek word kecharitomene. It therefore expresses a characteristic quality of Mary.
The traditional translation, "full of grace," is better than the one found in many recent versions of the New Testament, which give something along the lines of "highly favored daughter." Mary was indeed a highly favored daughter of God, but the Greek implies more than that (and it never mentions the word for "daughter"). The grace given to Mary is at once permanent and of a unique kind. Kecharitomene is a perfect passive participle of charitoo, meaning "to fill or endow with grace." Since this term is in the perfect tense, it indicates that Mary was graced in the past but with continuing effects in the present. So, the grace Mary enjoyed was not a result of the angel’s visit. In fact, Catholics hold, it extended over the whole of her life, from conception onward. She was in a state of sanctifying grace from the first moment of her existence.
For the mass on Saturday, I went to the 75th anniversary mass of the Diocese of Owensboro, KY. There were hundreds of people there to celebrate including all the priests and nuns in the Diocese. What I thought was cool too, was the bishop spoke in Spanish to the Catholic Hispanics. Seeing a bunch of Catholics in one place makes me happy! I'm glad I went!