Spiritually, the Ark was the manifestation of God's physical presence on earth. When God spoke with Moses in the Tent of Meeting in the desert, he did so from between the two Cherubs.
Once the Ark was moved into the Holy of Holies in the Tabernacle, and later in the Temple, it was accessible only once a year, and then, only by one person.
On Yom Kippur, the High Priest (Kohen Gadol) could enter the Holy of Holies to ask forgiveness for himself and for all the nation of Israel.
The Ark remained in the Temple until its destruction at the hand of the Babylonian empire, led by Nebuchadnezzar.
What happened to it afterward is unknown, and has been debated and pondered for centuries. It is unlikely that the Babylonians took it, as they did the other vessels of the Temple, because the detailed lists of what they took make no mention of the Ark.
