A.T. Robertson Commentary Revelation 21:5

"And he that sitteth on the throne said, Behold, I make all things new. And he saith, Write: for these words are faithful and true." — Revelation 21:5 (ASV)

Behold, I make all things new (Ιδου καινα ποιω παντα). 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 (Ιδου εγω ποιω καινα). The idea of a new heaven and a new earth is in Isa 65:17; 66:22; Psalms 102:25f. For the locative here with επ (επ τω θρονω) see 7:10; 19:4 (genitive more usual, 4:9f.; 5:1,7,13, etc.). See 20:11 for the picture.

And he saith (κα λεγε). Probably this means a change of speakers, made plain by μο (to me) in many MSS. An angel apparently (19:9f.) assures John and urges him to write (γραψον as in 1:11; 2:1,8,12,18; 3:1,7,14; 14:3). The reason given (οτ, for) is precisely the saying in 22:6 and he uses the two adjectives (πιστο κα αληθινο) employed in 19:11 about God himself, and 3:14 about Christ. In 19:9 αληθινο occurs also about "the words of God" as here. They are reliable and genuine.