Many of us have learned our understanding of the Bible from our Bible-believing brothers and sisters from outside the Catholic fold. At minimum we have been influenced by them. So we tend to see the Bible as a reference manual, or an instruction manual. What does the Bible say about a certain issue? Turn to this passage. Have a certain problem? Turn to that passage. One problem, one passage. But we lose sight that it is really a "Big Picture" kind of book. We have to remember that the Catholic way is to take all of scripture as a whole. This is the only way to see "The Plan."
Take, for instance, Catholics referring to Mary as the New Ark of the Covenant.
This is one of the more powerful examples of Typology in the Bible. And in the end it further supports Mary's sinlessness. Comparison between the Old Testament Ark of the Covenant and Mary exist on multiple levels. Most of us would be aware that the Ark of the Covenant carried the 10 Commandments. I would like to add the point that the Hebrews also referred to the 10 Commandments as the Decalogue, or 10 Words. The word for commandment can be translated as word. The Ark also carried Aaron's rod and a jar of manna. The 10 commandments represented the Law, Aaron's rod represented the priesthood and the manna was the life-sustaining bread that kept the Hebrews alive in the desert.
In the New Testament, Mary carried Jesus, our King and new law, and the Word, our High Priest, and the bread of life.
I could stop there. That's enough to make the point that Mary is the New Ark, isn't it? But the obvious is just scratching the surface.
In Exodus 40:34-35 "The cloud overshadowed the tent of the meeting and the glory of the Lord filled the tabernacle." The Greek word used here for overshadow is a form of episkaisei. In Luke 1:35 "The Holy Spirit will come upon you, and the power of the Most High will overshadow you; therefore the child to be born will be called holy, the Son of God." The Greek word for overshadow is episkaisei.
In 2 Sam 6:9 David asked how can the Ark come to me? In Luke 1:43 Elizabeth asked how does the mother of the Lord come to me?
In 2 Sam 6:11 the Ark remained in place for 3 months. In Luke 1:56 Mary remained with Elizabeth for 3 months.
In 2 Sam 6:5 David danced before the Ark. In Luke 1:41 John in Elizabeth's womb leapt for joy at the sound of Mary's voice.
God himself personally designed the Ark of the Covenant in Exodus 25. He designed it out of the purest and most precious materials, because it would be His own holy throne.
Significantly, since the Ark was to carry the presence of God, it was not only to be pure in all aspects, but protected in its purity. In Numbers 4:15-20 we see that God considered the Old Testament Ark of the Covenant so sacred that the high priest alone was given permission to touch it, or even to look inside it.
In 1 Sam 6, God slays 70 men of Bethshemes for merely looking inside the Ark.
Among the Levites (the priestly tribe) only a select sub-group, the Kohathites, were allowed to carry the Ark. Further, in Exodus 25:13-15, to carry the Ark, they had to use wooden staves overlain with gold that had been driven through golden rings on the outer edges of the Ark so that they would not come into contact with it.
In 2 Sam 6:7 Uzzah was helping to transport the Ark, when it became unstable and was about to fall to the ground. Uzzah touched the Ark to stabilize it, and in vs 8, God struck him down dead in his rashness. While his intentions may have been noble, it was in his own pride that he presumed himself to be purer than the earth.
God would not allow men in their state of sin to touch His holy throne.
This holy throne was an Ark made of acacia wood and gold. What then of a holy throne of flesh and blood?
Just as God Himself designed his Old Testament Ark, wouldn't he put as much, or more care in selecting the woman that would carry him within herself for 9 months, and then hold him and nurture him as a child, wouldn't He likewise select her to be pure, created from the "highest and purest" of substance and essence? Should not, then, the woman that would be his mother be spared from the stain of sin?
As we study scriptures typologically, we see over and over again that the Old Testament is merely preparing us for the New Testament. There is a reason for everything in the Old Testament, and the Old Testament is mirrored and magnified in the New Testament. The New Testament fulfillment is always greater than the Old Testament type.
When we look at how Jesus came into the world, there could have been so many different ways. Jesus's mother didn't need to be sinless. He could have been born in any number of situations. He could have been born to a wealthy woman, a Queen or, just as easily, he could have been born to a prostitute. That wouldn't change who Jesus was.
In fact Jesus didn't even need a mother. He could have done the "Star Trek" thing and just materialized all sparkly. When we speculate on these options, we must come to recognize that God chose this way. He chose to enter the world as a man, carried by a woman. And while she may not have needed to have been sinless, he chose to make his mother sinless because it was fitting. He created a narrative in the Old Testament, and would tie the scriptures together in the New Testament.
When we look at one verse or passage here, or another one there, you can see where someone might miss out on the Catholic understanding. But when you take the scriptures all together, we develop an understanding. Like the Ark before her, Mary also was pure and remained pure. She was sinless, and untouched. And God has made it abundantly clear to those that look at the big picture that this is how it was.