Today is a Holy Day of Obligation for Catholics. It is the feast of the Immaculate Conception - a commonly misunderstood doctrine.
I leave you with some great resources which explain the doctrine behind this feast day, including some excerpts.
Catholic Answers: Immaculate Conception and Assumption
The Marian doctrines are, for Fundamentalists, among the most bothersome of the Catholic Church’s teachings. In this tract we’ll examine briefly two Marian doctrines that Fundamentalist writers frequently object to—the Immaculate Conception and the Assumption.
Was Mary's Immaculate Conception Absolutely Necessary?
All the Immaculate Conception did was make Mary as Eve was before the Fall (precisely why the Fathers often called her the Second Eve or New Eve): unfallen and sinless; not subject to original sin. As Cardinal Newman remarked: why is it considered such an extraordinary thing that God chose to simply make one person -- the Mother of God the Son, the Theotokos -- the way that all of us would have been, but for the Fall? What better person to choose than the one who bore our Lord Jesus in her own body for nine months?! It makes perfect sense to me. I never had much difficulty with Marian doctrines once they were properly explained to me.
Fr. Martin Fox: Even Catholics get it wrong...
A lot of people think today’s feast—
the Immaculate Conception—
is about when Jesus was conceived.
That’s an understandable mistake to make.
But here’s the correct information:
the Immaculate Conception refers to
when Mary’s life began,
long before Jesus was born.
A beautiful photo on the blog of Fr. Zuhlsdorf
Jimmy Akin posts on the Immaculate Conception - and takes a "blogger day off" for the feast day. Mea culpa! for not doing the same.
And, as always, don't forget the Catholic Encyclopedia at New Advent