The Old Testament is filled with types, people and things which have importance for the Covenant of Moses, or Old Covenant, but which properly prepare for and foreshadow the perfect fulfillment of some spiritual reality in the New or Christian Covenant.
Thus, while the historical Ark of the Covenant carried the Word of God, in the Tablets of the Law, and was considered holy itself, being placed in the Holy of Holies of the Temple, Mary is the true Ark of the Covenant. She carried the Word Himself, the Bread of Heaven, and the Good Shepherd (Heb. 9:3-5; Rev. 11:19-12:1).
“Mary, in whom the Lord himself has just made his dwelling, is the daughter of Zion in person, the ark of the covenant, the place where the glory of the Lord dwells.” (Catechism of the Catholic Church 2676)
Thus, we see that the Old Testament, concerning the Ark of the Covenant (2 Samuel), and the New Testament, the Blessed Mother (St. Luke), use almost identical language.
And David was afraid of the LORD that day; and he said, “How can the ark of the LORD come to me?” - 2 Samuel 6:9
[Elizabeth said], “And why is this granted me, that the mother of my Lord should come to me?” - Luke 1:43
Michal … saw King David leaping and dancing before the LORD. - 2 Samuel 6:16
And when Elizabeth heard the greeting of Mary, the babe leaped in her womb. - Luke 1:41
And the ark of the LORD remained in the house of Obededom the Gittite three months. - 2 Samuel 6:11
And Mary remained with her about three months. - Luke 1:56
St. John in the Book of Revelation also reveals the connection between the Ark and the Blessed Virgin, stating:
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, loud noises, 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. (Revelation 11:19 – 12:1)