In Revelation the ark symbolizes the word standing up from the mercy seat to execute judgment upon the world. This is analogous to Israel's high priest exiting the holiest place after making atonement for the people on the day of atonement to send away Israel's sins on the goat of banishment. No man but the high priest could see the ark, and even then only through the glow of coals and a fog of smoke. So the temple being opened such that the ark is visible to all the world indicates their imminent destruction
Saying, We give thee thanks, O Lord God Almighty, which art, and wast, and art to come; because thou hast taken to thee thy great power, and hast reigned. And the nations were angry, and thy wrath is come, and the time of the dead, that they should be judged, and that thou shouldest give reward unto thy servants the prophets, and to the saints, and them that fear thy name, small and great; and that you shouldest destroy them which destroy the earth. And the temple of God was opened in heaven, and there was seen in his temple the ark of his covenant: and there were lightnings, and voices, and thunderings, and an earthquake, and great hail. Revelation 11:17-19