I can understand push-back from Protestants (of which I'm one) on the assumption,,,,even the Immac Concep (although I think that's pretty solid too)
I understand the human desire to read explicit statements such as "Mary was without sin" or "Mary's body was assumed into Heaven." But much about Mary remains veiled in Scripture. Even so, if we carefully consider what Scripture says about God and about Mary, I think there is still enough to point toward these beliefs.
For example, Scripture tells us that "Holiness befits your house, O Lord, forevermore" (Psalm 93:5), and Christ Himself teaches that "Blessed are the pure in heart, for they shall see God" (Matthew 5:8).
So how could the Woman chosen to be the earthly dwelling place of God the Word Incarnate be anything less than specially prepared and sanctified for such a vocation?
For that reason, it seems reasonable that She would have been made pure in body and soul for the vocation God had decreed for Her from all eternity. Through Isaiah, God foretold that
the virgin would conceive and bear a son. Mary was not an afterthought in God's plan.
Scripture also seems to present Mary as the New Eve.
Eve was created spotless, yet by her disobedience participated in humanity's fall. Mary, living not in Eden but in a fallen world, received God's messenger and answered,
"Let it be to me according to your word." Where Eve's "no" contributed to death, Mary's "yes" opened the way for the coming of the Savior. It is difficult for me to see this parallel as accidental.
Likewise, Luke's Gospel appears to present Mary as the New Ark of the Covenant. When David approached the Ark, he exclaimed,
"How can the ark of the Lord come to me?" When Mary came to Elizabeth, Elizabeth exclaimed,
"Why is this granted me, that the mother of my Lord should come to me?" David leapt before the Ark; John the Baptist leapt in his mother's womb before Mary. The Ark remained in the house of Obed-edom for three months; Mary remained with Elizabeth for about three months.
The old Ark carried the word of God written on stone, the manna from Heaven, and Aaron's priestly rod. Mary carried within Her womb the living Word of God, the true Bread from Heaven, and the eternal High Priest. If God commanded such reverence for the Ark that bore symbols of His presence, how much more would He prepare the woman who was to bear His presence Himself?
Yet Scripture also preserves Mary's own words:
"...my spirit rejoices in God my Savior." (Luke 1:46-47)
So how are these truths reconciled?
Mary indeed needed a Savior. Catholics do not believe otherwise. Rather, they believe She was saved in a unique way: not by being cleansed after falling into sin, but by being preserved from sin through the merits of Christ's future sacrifice. The physician who prevents a disease has saved just as surely as the physician who cures one.
Still, I feel any answer of my own falls short. While not Scripture, I find the following theological and poetic reflection beautifully expresses why Catholics see such holiness as fitting for the Mother of God:
"The Most Holy Trinity descended with Its perfections, inhabited with Its Three Persons, enclosed Its infinity in a small space. But It did not debase Itself by doing so, because the love of the Virgin and the will of God widened this space until they rendered it a Heaven. And the Most Holy Trinity made Itself known by Its characteristics:
The Father, being once again the Creator of the creature, as on the sixth day of Creation, had a real, worthy daughter fashioned to His perfect image. The mark of God was impressed so completely and exactly on Mary, that only in the Firstborn was it greater. Mary can be called the Second-born of the Father because, owing to the perfection granted to Her and preserved by Her, and to Her dignity of Spouse and Mother of God and Queen of Heaven, She comes second after the Son of the Father and second in His eternal thought, which ab aeterno took delight in Her.
The Son, being also "Her Son", did teach Her, by the mystery of Grace, His truth and wisdom, when He was but an Embryo, growing in Her womb.
The Holy Spirit appeared amongst men, for an anticipated prolonged Pentecost: Love for "Her Whom He loved", Consolation to men because of the Fruit of Her Womb, Sanctification on account of the Maternity of the Holy One.
God, to reveal Himself to men in the new and complete form, which starts the Redemption era, did not select for His throne a star in the sky, nor the palace of a powerful man. Neither did He want the wings of angels as the base of His feet. He wanted a spotless womb.
Also Eve had been created spotless. But she wanted to become corrupt of her own free will. Mary, Who lived in a corrupt world—Eve was in a pure world—did not wish to violate Her purity, not even with one thought remotely connected with sin. She knew that sin exists. She saw its various and horrible forms and implications. She saw them all, including the most hideous one: deicide. But She knew them solely to expiate them and to be, forever, the Woman who has mercy on sinners and prays for their redemption."