And He who sits on the THRONE said, "Behold, I am making ALL THINGS NEW."
When the first heaven and earth were created, everything God did was GOOD (Genesis 1:1-4-10-18-21-25-31). It was, in fact, "very good" until evil entered in. God in His purity and righteousness would not permit evil to go on forever, and thus He destroyed the first heaven and earth (Revelation 20:11 and Revelation 21:1). God is making ALL THINGS NEW. We know this is God doing it because He is the one sitting on the THRONE.
This is not a refurbishing of the first heaven and earth because the Greek word used for NEW, kainos, 'involves not only newness in time but also the freshness of having a completely different character.a This implies a new set of physical laws where entropy is set aside. ALL these NEW THINGS will last forever.
It is interesting to note that just as physicists and mathematicians have put forth theory after theory which is purported to describe how the first earth and heaven (universe) are put together, God will make a NEW CREATION. In Genesis, when the unified people wanted to become noted, they were scattered (Genesis 11:1-9).
And He said, "WRITE, for these words are FAITHFUL and TRUE."
This is a reminder of the first time John was told to "WRITE" (Revelation 1:11). Even as that "WRITE" was to the seven churches, this "WRITE", since it is in the same book of the Revelation of Jesus Christ, remains for the churches. We get the sense that John, even though he probably knew Jesus better than anyone, is so amazed at this NEW creation, he must be reminded to "WRITE".
While this ALL-THINGS-NEW concept is difficult for us to grasp, it is confirmed that the concept/reality is FAITHFUL and TRUE. The new heaven and earth will exist after all the tribulation judgments are done (Revelation 6-18), the 1,000 years reign of Christ is finished (Revelation 20:4-6), and all will have faced the great WHITE THRONE (Revelation 20:11-15).
One last observation: those whose names are in the Book of Life somehow are moved from the old earth to the new creation. Given that things of a spiritual nature do not have the physical movement restrictions we all know in this present earth, we can argue that this is entirely a spiritual creation. However, the new earth will have a dimensioned NEW JERUSALEM (Revelation 21:9-21). It apparently doesn't revolve around a NEW sun for there is no night there (Revelation 21:22-27). This implies that there is no concept of time; time is meaningless in eternity.
TRULY, this is a NEW THING!