Those powerful words from the Easter Exsultet often come to my mind at different parts of the year: "O blessed iniquity". It refers to the sin of Adam that brought about the need for our Savior to come and accomplish our redemption. One of the times that it comes to mind is when I begin to ponder the Immaculate Conception. Essentially, Adam and Eve were created "immaculate", and all the rest of humanity would have been as well if it had not been for their sin. That is not, however, the way things played out, and their choice to sin led to the need for a Savior.
Therefore, when we consider the Immaculate Conception and what it led to, then we can realize God's wisdom. Some have asked "why did God let Adam and Eve sin?" and wondered if He should have stopped them. Give some thought to what they were doing in their choice to sin. The devil came in the form of a serpent and tempted them; they saw the disobedience before them and chose to say "no" to God. You can almost hear Adam saying, "that sounds good, I want to decide for myself and try it that way".
For Mother Mary, however, there is a different story. If she had been conceived in sin and then been spoken to by Gabriel, she likely would have said, "no thanks, I'll pass". In her immaculate state, however, she heard the angel's testimony of what God planned for her life and said "yes". It was not, though, a "yes" in a vacuum. She was able to look at the sinful world around her (it must have been difficult to have never sinned, and yet still live in a world of sin) and say, "I've seen how much evil there is in the world, and I will joyfully submit to helping bring salvation to mankind".
Essentially, the fallen nature of the world enabled Mary, being sinless, to compare what the sin of Adam had brought, and decide to participate in conquering it. To have been conceived immaculate may seem like it is fraught with danger ("what if she sinned before Gabriel showed up?" as one protestant asked me), yet it was the very means that enabled her to see the world as God sees it. Even in our most holy moment we still do not hate sin like the Lord does. There is always this slight taint of temptation to it until we reach the beatific vision in Heaven. The Virgin did not have this. Instead she was able to see sin for what it truly was and realize how important it was to accept the calling God was giving her.
This is why the Immaculate Conception is vital for our salvation. This is why we must remember how important it is that God chose to do things exactly the way that He did; nothing He did fell short of perfect. So, this year when you fulfill your obligation and go to Mass on Immaculate Conception, give thanks to God that He is the one in charge, and that He granted us exactly what we need. Pray also that He would give to each of us to be able to see our own sins with holy eyes, precisely the way that He sees them. That is how we will turn away from them, and turn instead unto Christ our Redeemer.