In the deepest insides of Moses’ temple, in the Most Holy Place behind the veil, stood the ark of the covenant. It was called the ark of the covenant
because a copy of the law God gave at Mount Sinai was placed in the ark as a lasting testimony of the relation between God and Israel (Exodus 25:16; Exodus 40:20; see also Hebrews 9:4). Over the ark was a mercy seat (Exodus 25:21–22) which functioned as God’s throne among his people (see 1 Samuel 4:4; 2 Samuel 6:2; Psalm 80:1; Psalm 99:1). That throne symbolized the heavenly throne John saw in Revelation 4:2. With the opening of the temple, this throne would now be publicly visible.
19 Then God’s temple in heaven was opened, and the ark of his covenant was seen within his temple. There were flashes of lightning, rumblings, peals of thunder, an earthquake, and heavy hail.