Feast of the Immaculate Conception

I attended Mass last night as I was singing with Una Vocis.  It had been a few years since I had attended a Catholic Mass, and I'm still a bit confused on all the things "insiders" know about the liturgy.

Yesterday was the Feast of the Immaculate Conception.  For you Protestants, not that one.  This is the one celebrating Mary's immaculate conception.  Catholic doctrine holds that Mary, by virtue of her selection to be Jesus' Mother was kept pure from all sin, including original sin.  This doctrine is old, but was not official dogma until fairly recently, as far as Christian doctrine goes.

The dogma of the Immaculate Conception of Mary was promulgated in 1854 by Pope Pius IX.  This doctrine was one debated for centuries.  Luther originally celebrated the feast as a monk, but later rejected the doctrine.

At first, my reaction was that this was a concocted idea, but after some research, it does have some interesting implications.  First, does it imply that Mary did not need a redeemer?  If she was born without sin and was without sin until Jesus' birth, how does that figure into the idea that "All have sinned?"

It makes me think more about Mary - what about her set her apart so that God chose her to carry His Son?  How did a simple girl from the countryside of Israel come to be the most blessed mother ever?