16 The 24 elders, who were seated before God on their thrones, fell facedown and worshiped God,
“The 24 elders” are believers that might represent the 12 tribes of Israel and the 12 Apostles.
God was worshipped by the 24 elders who saw God’s justice displayed on the earth.
17 saying: We thank You, Lord God, the Almighty, who is and who was, because You have taken Your great power and have begun to reign.
The phrase “who is and who was” is a reference to the Alpha and Omega as seen in Revelation 1:8. In verse 18 of chapter 1 of Revelation, it gives a more specific meaning of the phrase.
“Who is” means the Living One or the I Am (Exodus 3:14-15, John 8:58)
“Who was” means His death on the cross but in Revelation 1:8 it adds “who is coming” which is the second advent of Christ.
“have began to reign” refers that Satan’s power on earth is dwindling and Jesus millennial reign will commence very soon.
18 The nations were angry, but Your wrath has come. The time has come for the dead to be judged and to give the reward to Your servants the prophets, to the saints, and to those who fear Your name, both small and great, and the time has come to destroy those who destroy the earth.
The anticipation in heaven to see Jesus reign on earth for the 1000 years is great. The heavenly host has seen the destruction of Satan and his fallen angels have caused to the human race but now finally justice for all the evil that was done is quickly approaching.
19 God’s sanctuary in heaven was opened, and the ark of His covenant appeared in His sanctuary. There were flashes of lightning, rumblings of thunder, an earthquake, and severe hail.
“the ark of His covenant appeared in His sanctuary” was to show the people of all nationalities who have rejected Christ have broken His covenant law by worshiping false gods.
The earthquake and the severe hail is in response to rejecting Jesus as their Lord and God (John 20:28).