Chapter twenty-one begins with the present universe and earth having been removed or destroyed.
A new universe and a new earth have been created for life in the eternal state. The New Jerusalem, heaven, the city of God, descends into this universe and this is the eternal state of mankind and the eternal God.

Or, chapter 21 and 22 could be describing the millennial state on the earth since verses in other places in the Scripture that deal with the New Heaven and the New Earth are descriptions of the Millennial Kingdom:“

" 'Behold, I will create new heavens and a new earth.
The former things will not be remembered, nor will they come to mind.
But be glad and rejoice forever in what I will create,
for I will create Jerusalem to be a delight and its people a joy.
I will rejoice over Jerusalem and take delight in my people;
the sound of weeping and of crying will be heard in it no more.
Never again will there be in it an infant who lives but a few days, or an old man who does not live out his years;
he who dies at a hundred will be thought a mere youth;
he who fails to reach a hundred will be considered accursed.
They will build houses and dwell in them; they will plant vineyards and eat their fruit.
No longer will they build houses and others live in them, or plant and others eat.
For as the days of a tree, so will be the days of my people;
my chosen ones will long enjoy the works of their hands.
They will not toil in vain or bear children doomed to misfortune;
for they will be a people blessed by the Lord, they and their descendants with them.
Before they call I will answer; while they are still speaking I will hear.
The wolf and the lamb will feed together, and the lion will eat straw like the ox, but dust will be the serpent’s food.
They will neither harm nor destroy on all my holy mountain,' says the Lord."
- Isaiah 65:17-25

" 'As the new heavens and the new earth that I make will endure before me,' declares the Lord, 'so will your name and descendants endure. From one New Moon to another and from one Sabbath to another, all mankind will come and bow down before me,' says the Lord.  'And they will go out and look upon the dead bodies of those who rebelled against me; their worm will not die, nor will their fire be quenched, and they will be loathsome to all mankind.' ” - Isaiah 66:22-24

"The Lord is not slow in keeping his promise, as some understand slowness. He is patient with you, not wanting anyone to perish, but everyone to come to repentance. But the day of the Lord will come like a thief. The heavens will disappear with a roar; the elements will be destroyed by fire, and the earth and everything in it will be laid bare. Since everything will be destroyed in this way, what kind of people ought you to be? You ought to live holy and godly lives as you look forward to the day of God and speed its coming. That day will bring about the destruction of the heavens by fire, and the elements will melt in the heat. But in keeping with his promise we are looking forward to a new heaven and a new earth, the home of righteousness."
- 2 Peter 3:9-13

"… what the situation will be like in the world before the Lord returns, namely, Christ will be despised,
and the preachers of the Gospel
will be regarded as fools."

- Martin Luther, 1520

Most Americans think the
Ten Commandments are
valid rules for living, but many
have a rough time recalling
exactly what those rules are.

Among teenagers, 3 in 10
do not know the significance of Easter for Christians;
among teenagers who attend church regularly, 2 in 10
do not know it.