I do not believe it to be coincidental that John's vision moved directly from the Ark to the Woman. Both are images of the Virgin Mary.
Now the Ark was the holiest object under the Old Covenant. It was the golden chest that contained the Tablets of the Ten Commandments, the staff of Aaron (the first high priest), and sample of the "heavenly bread," manna, the Israelites ate in the desert. It was God's earthly throne; the Lord was said to sit enthroned upon the cherubim atop the Ark. When Israel's priests carried the Ark into the Jordan River it parted, just as the waters of the Red Sea had, allowing the Israelites to enter the Promised Land. After it was carried in procession for seven days around the city of Jericho, the city's walls collapsed.
In the New Testament, when the angel Gabriel appeared to Mary, he told her,"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 (Lk 1:35). "Overshadow" - it was the same term used to describe God's coming to dwell in the Tabernacle and Temple when the Ark was placed in their Holy of Holies.
It's fascinating to see how Luke developed this insight in his telling of Mary's visit to her kinswoman Elizabeth. Allow me to set it next to the Old Testament's account of David bringing the Ark of the Covenant to his newly won capital, Jerusalem.
The Ark was a type, a prophetic symbol, of the Virgin Mary. The original Ark contained the Ten Commandments, high priest's staff, and manna; but Mary's womb contained Jesus - the Word of the Father, our great High Priest, and the true "Bread of Life." Mary's lap was the only throne our Lord knew during His earthly life! The holiness of the Ark, the way it was completely set apart for the service of God (note above how Uzzah died simply from touching it), prophesied the holiness of Our Lady.
Recall how the angel Gabriel began his message to Mary, “Hail, full of grace, the Lord is with you!...Do not be afraid, for you have found favor with God” (Luke 1:28,30). “Full of grace,” or “O favored one,” in some versions of the Bible, is a translation of the Greek term “Kechari-tomene.” It refers to an absolute plentitude of grace, Mary “‛has been’ and ‘is now’ filled with divine life.” There was never a moment of separation between she and God. This belief is what Catholics mean when they speak of her “immaculate conception.”
Mary, like all of us, had to be saved from sin. She herself said, “my spirit rejoices in God my Savior” (Luke 1:47). She was saved from sin – only the manner differs.
Jesus' offering to the Father cuts forwards and backward in time; He is the "lamb slain from the foundation of the world" (1 Pet 1:19-20). His sacrifice is the source of salvation for people from the beginning of history all the way through its end (Heb 9:28; Rev 13:8; 1 Pet 3:19-20). You and I received God's grace into our souls after we had already contracted original sin; but in Mary's case, the fruits of Jesus’ victory were applied at conception, saving her from ever contracting original sin. Now, if John the Baptist could respond to the Holy Spirit while in his mother’s womb (see Lk 1:41,44 above), then how can we object to Mary receiving the Spirit but a few months earlier, at conception? Mary had no way to earn this gift; it was granted at the instant she came into being. Nor was it a requirement to bear the sinless Jesus. It was certainly fitting, but not a requirement. It was God’s sovereign choice, His free gift.