As Mark Shea notes, the theological gap between Catholics and Protestants is, in one particular regard, quite wide. Whereas Protestant — especially evangelical — theology tends to focus on Scripture, verbal confession of faith, and the action of the Spirit, Catholic Theology tends to focus on contemplation, the human person, and (of course) Eucharist. To an evangelical, prayer is supposed to be a means of achieving something. To a Catholic, prayer is meant to draw us closer into unity with God.

And in a certain way, the difference between Catholics and Protestants can be abstracted in the difference between women and men. Evangelicalism and Protestantism0 tend to be a more masculine expression of faith, while Catholicism tends toward the feminine (no doubt inspired by the Biblical image of the Church as the bride of Christ). The misunderstandings we have of each other tend to follow the same lines.

Perhaps it's no surprise, then, that while Protestants and evangelicals tend to favour St. Paul as their example of witness, Catholics tend to favour Mary as the ideal Christian model (remember: Jesus can't show us how to be a disciple of Jesus; only a follower of Jesus can do that). And of course, at the heart of the Marian example is her assent to God's plan in her saying "let it be done to me" to the angel, when the angel announced that she was to bear the Son of God.

I think we can all accept it to be true that, were it not for Paul's considerable efforts, the Gospels would never have reached the Gentiles. No earnest Christian could disagree with this statement. But far too many Christians disagree with another equally reasonable statement: that without Mary, Christ would not have been born; the Gospels, then would never even have come to Earth!

I've heard all manner of responses to this before, most of which tend to be variants on "oh, God would have just chosen someone else." To such a speaker, Mary is merely a life-support system for her uterus, a hot-swappable piece of hardware that can be disposed of at a later date when no longer necessary.

It is odd to hear such a view espoused by supposedly "Biblical" Christians, because such a view plainly contradicts Scripture. We come back to Luke 1 again:

[26] In the sixth month the angel Gabriel was sent from God to a city of Galilee named Nazareth,

[27] to a virgin betrothed to a man whose name was Joseph, of the house of David; and the virgin's name was Mary.
[28] And he came to her and said, "Hail, O favored one, the Lord is with you!"

Again, it serves to note that the term "o favoured one" is often translated as "full of grace", and denotes that Mary herself was possessed of the sanctifying grace of the Lord at the outset. The specific term translated from Greek — kecharitomene — is the "passive participle of charitoo and means endowed with grace (charis), enriched with grace as in Ephesians. 1:6,…The Vulgate gratiae plena "is right, if it means 'full of grace which thou hast received'; wrong, if it means 'full of grace which thou hast to bestow'". The translation of this word is undisputed across the broad spectrum of Christian denominations, and is a part of all common extant translations of the Bible.

In other words, we all agree on one thing, at least: Mary was indeed full of grace, and highly favoured of God. But the specific kind of grace she was endowed with was sanctifying grace, the salvific grace of God that is the basis of justification (c.f. Romans 5:20-21). We might thus construct a logical analysis thusly:

Premise: The Bible teaches that we are saved by the grace of God alone.
Premise: To be full of the grace of God is, thus, to be saved

Observation: Mary was full of the grace of God (c.f. Luke 1:28)

Conclusion: Mary, being full of grace (premise #1) is thus in a state of salvific sanctification (premise #2).

What does this mean? Well, for starters, it speaks to the uniqueness of Mary in God's plan, and why no other woman would do. Mary was appointed, by God, for the task of bearing the Son. She was preserved from all sin by the sanctifying grace of God. And yet she was not an automoton; to the last moment, God left the decision as to whether or not she would bear the son in Mary's hands; the angel appeared to announce the news to her, yes, but also to receive her consent (Luke 1:38).

And absent the consent of Mary, absent her saying "behold, I am the handmaid of the Lord; let it be to me according to your word," we don't have Christ. Not in the flesh, at any rate. We do have the Logos, the Word, the second person of the Holy Trinity. But we don't have Jesus, the man who lived and who died, and who rose again to fulfill the Scriptures and bring salvation to all the nations.

Would God have simply chosen another, had Mary not given her assent? Is that to say, then, that another young, virginal woman existed who was already full of the sanctifying grace of the Lord? No, the very suggestion is absurd on its face, and the angel's greeting makes it very clear that Mary has been chosen and called by name. Moreover, in the Magnificat (the name given to Mary's testimony to Elizabeth, later in Luke 1), Mary confesses:

[46] And Mary said, "My soul magnifies the Lord,
[47] and my spirit rejoices in God my Savior,
[48] for he has regarded the low estate of his handmaiden.
For behold, henceforth all generations will call me blessed;
[49] for he who is mighty has done great things for me,
and holy is his name.

The Spirit desired us to know that Mary is blessed of God, and (moreover) that Mary is to be seen as, and called, "blessed" by every Christian. This is no interchangeable uterus-support system we are talking about here: this is a unique woman, solely chosen of God to give birth to the Saviour. Had she refused, there was no other.

Mary's "yes" to God was the first participation of a human being in the salvific plan of God, and was the first step by which our salvation was secured. She was the Mother of the Son. Mary, alone amongst all women, gave us Jesus, and only Mary, alone amongst all women, could have given us Jesus.

Had she refused the angel, we would likely all still be living under the Old Covenant. Food for thought.