11:19And the temple of God which is in heaven was opened; and the ark of His covenant appeared in His temple, and there were flashes of lightning and sounds and peals of thunder and an earthquake and a great hailstorm.

And the temple of God which is in heaven was opened;

The Revelation of Jesus Christ is an "opening" book:

Door opened Revelation 4:1
Seals opened Revelation 6:1-9
Abyss opened Revelation 9:2
Heaven opened Revelation 19:11
The books opened Revelation 20:12

What has been hidden from us and the earth in the spiritual realm is slowly revealed. With the revelation comes an awareness of God's purity and holiness. The result of the encounter with purity and holiness is judgment against sin and the devil (Revelation chapters 12-16).

Since the temple is the place of worship, this encounter is a worshipful experience. John saw parts of this temple previously: throne and sea of glass (Revelation 4:6); and altar (Revelation 6:9, Revelation 8:3-5); and service by tribulation saints (Revelation 7:15).

Isaiah saw the throne and temple in Isaiah 6:1. Paul indicates this temple is where Christ now is ministering as High Priest (Hebrews 8:1-7). Recall, Christ as the untimate sacrifice is able to be this High Priest, Hebrews 9:23-26.

and the ark of His covenant appeared in His temple;

The ark with its mercy seat (Exodus 37:1-9) speaks to atonement for sin. Thus this typifies Christ; the law, manna, and Aaron's rod contained therein show man's dependence/imperfection with respect to God.

In the Old Testament, the last reference to the ark occurs in 2 Chronicles 8:11. Later, Solomon with his involvment with Pharoah's daughter, Queen Sheba (Ethiopian), gave "all her desire (2 Chronicles 9:12) including perhaps the Ark. Ethiopian history claims the Ark is guarded in a church in Aksum, Ethiopia.

Isaiah has a prophesy in Isaiah 18:1-7 which may indicate the return of the ark. The 'standard' in verse 3 (nes in Hebrew) could be translated as 'ark'. Likewise, the 'gift' (nes, again) in verse 7 is returned 'to the place of the name of the Lord of hosts'.

and there were flashes of lightning and sounds and peals of thunder and an earthquake and a great hailstorm.

Compare this to events at the temple at Christ's death, Matthew 27:51.