Mary, the Ark of the New Covenant

In the comments, Waterloo Region African asked how early Christians thought of Mary as the New Ark.  I think that the best answer is that St. Luke lays this out pretty clearly in the first chapter of his Gospel.  He draws some incredibly obvious parallels between Mary's visit to Elizabeth and David's movement of the Ark through the hill-country of Judah. These are ones that a well-read Jewish audience should have been able to pick up on, and it helps reveal who Luke is telling us Jesus is, as well as the role he says Mary plays.

Start with the Old Testament passage.  From 2 Samuel 6:2-14:

And David arose and went with all the people who were with him from Ba'ale-judah, to bring up from there the ark of God, which is called by the name of the LORD of hosts who sits enthroned on the cherubim.

And they carried the ark of God upon a new cart, and brought it out of the house of Abin'adab which was on the hill; and Uzzah and Ahi'o, the sons of Abin'adab, were driving the new cart with the ark of God; and Ahi'o went before the ark. And David and all the house of Israel were making merry before the LORD with all their might, with songs and lyres and harps and tambourines and castanets and cymbals. And when they came to the threshing floor of Nacon, Uzzah put out his hand to the ark of God and took hold of it, for the oxen stumbled. And the anger of the LORD was kindled against Uzzah; and God smote him there because he put forth his hand to the ark; and he died there beside the ark of God. And David was angry because the LORD had broken forth upon Uzzah; and that place is called Pe'rez-uz'zah, to this day.

And David was afraid of the LORD that day; and he said, "How can the ark of the LORD come to me?" So David was not willing to take the ark of the LORD into the city of David; but David took it aside to the house of O'bed-e'dom the Gittite. And the ark of the LORD remained in the house of O'bed-e'dom the Gittite three months; and the LORD blessed O'bed-e'dom and all his household.

And it was told King David, "The LORD has blessed the household of O'bed-e'dom and all that belongs to him, because of the ark of God." So David went and brought up the ark of God from the house of O'bed-e'dom to the city of David with rejoicing; and when those who bore the ark of the LORD had gone six paces, he sacrificed an ox and a fatling. And David danced before the LORD with all his might; and David was girded with a linen ephod.

Here are the seven things to notice:

1. David “arose and went” to move the Ark.
2. They're in Judah (they start out from Baale of Judah)
3. They're in the hill country: Abinadab's house is on one of these hills, and it's navigating these hills that causes the ox to stumble, the Ark to totter, and Uzzah to touch the Ark, which causes God to strike him dead.
4. David, vexed by the death of Uzzah, asks, “How can the ark of the LORD come to me?”
5. Obededom and his household are blessed by the presence of the Ark. 
6. David dances before the Ark.
7. The Ark stays with Obededom for three months.

Compare this with Luke 1:39-45,56 (I'm skipping over the beautiful Magnificat for the sake of brevity):

In those days Mary arose and went with haste into the hill country, to a city of Judah, and she entered the house of Zechari'ah and greeted Elizabeth. And when Elizabeth heard the greeting of Mary, the babe leaped in her womb; and Elizabeth was filled with the Holy Spirit and she exclaimed with a loud cry, "Blessed are you among women, and blessed is the fruit of your womb! And why is this granted me, that the mother of my Lord should come to me? For behold, when the voice of your greeting came to my ears, the babe in my womb leaped for joy. And blessed is she who believed that there would be a fulfilment of what was spoken to her from the Lord." [...] And Mary remained with her about three months, and returned to her home.

And again, the seven things to notice:

1. Mary “arose and went” to transport her and her Son to the household of Elizabeth.
2. They're in Judah.
3. They're in the hill country.
4. Elizabeth's question mirrors David's, but is asked out of joy, rather than vexation: “And why is this granted me, that the mother of my Lord should come to me?”
5. Elizabeth is blessed by the presence of Mary (“the mother of my Lord”).
6. John the Baptist dances in the womb upon hearing Mary's greeting.
7. Mary stays for three months.

So both Mary and David “arose and went” on these journeys, to the same place (the hill-country in Judah) for the same length of time (three months).  David dances before the Ark, and John the Baptist dances before Mary.  David asks, “How can the ark of the LORD come to me?” Elizabeth asks, “And why is this granted me, that the mother of my Lord should come to me?”  And Elizabeth was blessed to be visited by the Mother of the Lord, just as Obededom was blessed to be visited by the Ark.

Now, St. Luke chose to include all of those minor details (including that it was the hilly country, and that Mary stayed for three months) for a reason.   Likewise, he chose to words things in the precise way that he did for a reason - to say that she “arose and went,” for example (the only time he uses this Old Testament expression in his Gospel).

There are three reasons that it makes sense for Luke to choose this particular passage (2 Samuel 6), of all the Old Testament descriptions of the Ark, to show the parallel to Mary:

• It reminds us that even at this point, immediately after the Annunciation, Mary is carrying Jesus Christ. 2 Samuel 6:2 reminds us that it is “the LORD of hosts who sits enthroned on the cherubim.”  That's an important reminder, in the middle of a chronological retelling of a series of events.
• It's our first hint that Jesus Christ is Lord.  Again, the Ark contained the enthroned LORD of hosts.  If Mary is the new Ark, that means that Jesus is the enthroned LORD of hosts.  We take this for granted today.  At the time Luke is writing, it's a shocking claim.
• It shows how Mary is set aside by God.  This is the exact passage in which Uzzah is struck dead for touching the Ark.  This helps explain Mary's consecrated Virginity -- her strange response in Luke 1:34, for example, or the fact that the Isaiah 7:14 prophesy required the Christ to be both conceived and born of a Virgin, when a Virgin conception would have been sufficient to establish the miracle.  These odd details make perfect sense if Mary is the new Ark.  

Ark of the Covenant Monstrance at
St. Stanislaus Catholic Church, Chicago

Nor is St. Luke the only one New Testament writer to have this insight. In Revelation 11:19-12:2, here's what John sees:

Then God's Temple in Heaven was opened, and the Ark of His Covenant was seen within His Temple; and there were flashes of lightning, voices, peals of thunder, an earthquake, and heavy hail. And a great portent appeared in heaven, a woman clothed with the sun, with the moon under her feet, and on her head a crown of twelve stars; she was with Child and she cried out in her pangs of birth, in anguish for delivery.

Sure enough, this woman “brought forth a Male Child, One who is to rule all the nations with a rod of iron” (Rev. 12:5).  That is, we're dealing with the Mother of Jesus here.  It's true that this passage likely refers to the Church as well as Mary,  But once you read Luke 2, it's hard to avoid the conclusion that it's not for nothing that John is shown the Ark immediately before being shown the Mother of God.

For more on this subject, there's a helpful article here.  It includes other interesting details, like the connection between the “overshadowing” of Mary in Luke 1:35 and the overshadowing of the Shekinah Glory Cloud in the Old Testament.