Surely, there are many reasons why Mary was immaculately conceived, some of which we may never truly know or understand until we obtain heavenly perfection, but Mary's immaculate conception is a necessary piece of our own redemption.
I think of Jesus never knowing sin. So, while He was in the womb of Mary, He did not experience the stain of sin, since Mary had none within her. Babies in the womb share so much with their mother, even to the point that a mother always has some of the cells of their children with them throughout their life.
Then, there is the example of Adam and Eve. God began human existence with two sinless people and it seems only fitting that God began things anew with two sinless people.
But, if Jesus is our Lord and Savior, what was Mary’s role? Nothing can take away from what Jesus did for us. Indeed, Mary’s role in our salvation does not take away from what Jesus did for us. No, it only adds to it.
While Jesus hung on the cross, Mary accepted it and offered her suffering up to God in union with her son’s suffering. Not only did she accept becoming the Mother of God, but being completely free from sin, she was able to do this completely. Then, while Jesus hung on the cross, she accepted being the Mother of the Body of Christ, the Church and all of its members. Being free from sin, she was able to fulfill her role in salvation history. A role that I depend upon everyday.
Thank you, Mary, for your acceptance and thank you, God, for giving us a perfect Mother.