Some people ask in the 21st century what difference does it make whether or not the Mother of God was born without original sin? On one level they are correct, had it been God's will he could have been born of the lowliest most sinful woman in the world.
All of the miracles of Jesus are important not in themselves but for what they teach us. The healings, even raising Lazarus from the dead were only momentary events. After all, did not all these people eventually pass from this life as we will? Lazarus is not still here.
The point of each of the miracles was to teach us something about God and his plan for the human race.
One of the many things we learn from the Immaculate Conception is that there are no accidental people. My birth mother was 16 year old high school girl. She may have never intended to get pregnant. She may have thought that getting pregnant with me ruined her life. And I have no doubt she was traumatized. But from the moment God created my soul and placed it in my microscopic body God had a plan for me. God saw how I fit into his universe.
And so it is that God participates in the creation of every human being. In the case of Mary, being conceived without original sin was a unique gift she needed to fulfill her role in the plan. But God does the same with each of us. God gave you the gifts you need to fulfill your place in the world.
People ask why the Church seems "obsessed with sex." For us, sex is meant to be this magnificent collaboration between a man a woman and God, out of which come a unique new person. Each person is born with a unique mission, each born with a unique combination of gifts. Even so called identical twins are not truly identical.
Today as we celebration the moment Mary was conceived offers us a chance to reflect on each human life, including our own. And give thanks to God.