Today is the Feast of the Immaculate Conception, when we honor Mary, conceived without original sin. As a young Catholic, I had always simply accepted this status for Mary without much thought to the theological reasoning behind it. When I began studying the Catholic faith in earnest (around the time of my wife’s conversion), I reflected more deeply on why Mary was granted such a privilege to be without sin since the moment of her conception.
Original sin is passed from parent to child – it is inherited. Because of humanity’s fall, we are all conceived in this state, which damages our relationship with God. Because of original sin, we are all in need of salvation. There is nothing in our power that we can do to overcome this fall from grace. Only an act of God can save us. We are cut off from God and in need of His saving grace.
Mary was saved by just such an act of God. She was preserved from original sin so that she would be spotless, the perfect vessel for carrying God’s Son. The reason this was theologically necessary is quite simple. If Mary had possessed original sin, she would have passed it on to Jesus, her child. Jesus would then inherit a fallen human nature.
To prevent this, God could have “stepped in” at the moment of Jesus’ conception to "save” Him from original sin. But can you imagine a Savior in need of salvation?…the Son of God in need of grace? This is obviously not a workable solution. If Jesus had been in need of salvation at the time of His conception, He would not be God.
In order for Jesus' divinity to not be in jeopardy, it must be that He inherited a perfect humanity from His mother Mary. And so Mary was spared through God's grace so that Jesus would be born naturally without the stain of original sin. It was not an act of Mary that caused this…she still owes her salvation to God, as we all do...but without this singular act of God’s grace bestowed on Mary the birth of the God-made-man would have been a theological impossibility. Mary was spared from original sin so that Jesus (who is God) could be born without the need of salvation, and He could then offer himself unblemished as a sacrifice for us all.