{Behold, I make all things new} (Idou kaina poi(9320)panta).
The first time since  1:8  that God has been represented as
speaking directly, though voices have come out of the throne
before ( 21:3 ) and out of the sanctuary ( 16:1,17 ), which may
be from God himself, though more likely from one of the angels of
the Presence. This message is not addressed to John ( 7:14  17:7  21:6  22:6 ), but to the entire world of the blessed. See  Isa
43:18f.  for the words (Idou eg(9320)poi(9320)kaina). The idea of a new
heaven and a new earth is in  Isa 65:17  66:22  Ps 102:25f . For
the locative here with epi (epi t(9369) thron(9369)) see  7:10  19:4 
(genitive more usual,  4:9f.  5:1,7,13 , etc.). See  20:11  for
the picture. {And he saith} (kai legei). Probably this means a
change of speakers, made plain by moi (to me) in many MSS. An
angel apparently (as in  14:13  19:9f. ) assures John and urges
him to write (grapson as in  1:11  2:1,8,12,18  3:1,7,14  14:3 ). The reason given (hoti, for) is precisely the saying in
 22:6  and he uses the two adjectives (pistoi kai al(8874)hinoi)
employed in  19:11  about God himself, and  3:14  about Christ.
In  19:9  al(8874)hinoi occurs also about "the words of God" as
here. They are reliable and genuine.