For many, the doctrine of the Immaculate Conception is the hardest to believe of all the Church’s teachings. The idea of Mary having been completely sinless can be hard to believe and even misinterpreted.

That’s why knowing how to explain it to skeptics is so important.

Let’s start with some background.

Pope Pius IX infallibly defined the dogma of the Immaculate Conception on Dec. 8, 1854.

“The Most Holy Virgin Mary was, in the very first moment of her conception, by a unique gift of grace and privilege of Almighty God and in view of the merits of Jesus Christ the Redeemer of mankind, preserved free from all stain of original sin.” (Ineffabilis Deus, Apostolic Constitution of Pope Pius IX on the Immaculate Conception)

And what exactly does that mean?

It means that, from the moment she existed, she was preserved from original sin. Consequently, she also was preserved from the stain, or effects, of original sin. Because of that, her nature was not corrupt in any way.

Why was Mary given this privilege? Because of her connection to our Lord. She was his Mother and at the same time he was her Savior. As Catholics, we believe that Mary was proactively redeemed. In other words, she received the fruits of Christ’s redemption prior to her conception. Remember that our concept of time is not like God’s concept—or governance—of time. With him all things are possible, and he has the power to extend redemption to Mary before she was conceived in the womb of St. Anne. The Church also teaches that Mary was free from personal sin as well because her nature was spotlessly incorrupt as result of her Immaculate Conception.

Skeptics may tell you that the doctrine of the Immaculate Conception is not found in Scripture. They might cite St. Paul’s Letter to the Romans in which he wrote, “all have sinned and fall short of the glory of God.” But in this case, St. Paul is referring to personal sin, which Mary was unable to commit because of her proactive redemption. Mary’s preservation from original sin didn’t remove her need for a redeemer. She needed a redeemer, but she was granted a more perfect redemption.

Duns Scotus, a 13th-century English Franciscan theologian, used the image of quicksand to explain Mary’s more perfect redemption. If someone pulled you out of quicksand after you’d fallen in, you’d say that he saved you. If this person kept you from falling into quicksand, you’d say that he saved you more perfectly.

Now look to another place in Scripture—to the Gospel of St. Luke. How does the Angel Gabriel greet Mary?

“In the sixth month the angel Gabriel was sent from God to a city of Galilee named Nazareth, to a virgin betrothed to a man whose name was Joseph, of the house of David; and the virgin’s name was Mary. And he came to her and said, “Hail, full of grace the Lord is with you!” But she was greatly troubled at the saying, and considered in her mind what sort of greeting this might be. And the angel said to her, “Do not be afraid, Mary, for you have found favor with God. And behold, you will conceive in your womb and bear a son, and you shall call his name Jesus.” (RSVCE, Lk 1:26-31)

If Mary had been touched by sin, Gabriel wound not have pointed out that she was “full of grace.” Any sinfulness at all diminishes grace in a soul. By his greeting, the Angel is acknowledging that Mary has attained the fullness of grace and is free from all sin.

St. Ephraim of Syria (c. 306-373) is a prominent Father and Doctor of the Church. He’s a noted authority on many of the Church’s teachings. Regarding Mary’s sinlessness, he wrote:

You [Christ] alone and your Mother
Are more beautiful than any others;
For there is no blemish in you,
Nor any stains upon our Mother.
Who of my children
Can compare in beauty to these?
(The Nisibene Hymns, 27, 8)

The Immaculate Conception makes absolute sense to me. When I’m asked about it, my first line of defense, so to speak, is this and it’s based on my own reasoning.

Jesus Christ is the God-Man, the Word Incarnate. He is All-Powerful, All-Knowing, All-Perfect, and is opposed to sin in all forms. How then, could he have been conceived and born from an imperfect womb that had been touched by sin? I would find that truly hard to believe.