Revelation 1V18ff:"I am he that liveth, and was dead; and, behold, I am alive for ever more, Amen; and have the keys of HELL and of DEATH."
If you pay close attention, to what Jesus is saying here--he says "of Death"
Revelation 20:12, 14:The "dead" are the unbelieving dead of all the ages - the "rest of the dead" mentioned in verse 5
They are "judged" from two sets of books.
The "books" contain the record of every unsaved person's life.
Each unsaved person is judged according to his "works".
Every human being is guilty and deserving of "death".
The "book of life" contains the name of every person who has received eternal LIFE through FAITH ALONE (John 20:31)
"Death and hell (Hades) are the temporary holding places of unsaved men's bodies and souls, respectively (Luke 16:19-31).
The "Second Death" is eternal punishment in the "lake of fire," experienced only by the unsaved.
Once the final judgment occurs, there is no further need for either Death or Hell (Hades) ETERNAL SEPARATION is now made between those who have LIFE and those who have "death" Dan.12:3; John 5:29).
The Scriptures never refer to death as the MERE CESSATION of LIFE, but instead as the UNNATURAL SEPARATION of something from that to which it belongs.
Therefore, a body without the SPIRIT suffers Physical death (Gen. 35:18).
The expression "second death" defines the separation of man from God,
Human consciousness is conveyed in the biblical description of Second death, suggesting that the beast and the False Prophet will both remain alive for a 1000 years after being cast into the lake of fire (Rev.19:20; 20:10)
When a person is saved, he has passed from death to life, and an be assured he will never come into condemnation (John 5:24)
The right perspective of death is this: Jesus Christ and God has ALL POWER over death and life.
God can allow life on earth for any individual or angelic being--as long as He sees fit--and should not be seen as physical cessation of life.
The Angel of Death-or the Four Horsemen of the Apocalypse are just doing the bidding of God--which is delivering death sentences and making sure God's commands are carried out--they are just messengers nothing more.
Revelation 20V14:"And death and hell were cast into the lake of fire. That is the second death."