A.T. Robertson Commentary Revelation 21:1

"And I saw a new heaven and a new earth: for the first heaven and the first earth are passed away; and the sea is no more." — Revelation 21:1 (ASV)

A new heaven and a new earth (ουρανον καινον κα γην καινην). This new vision (ειδον) is the picture of the bliss of the saints.

The first heaven and the first earth (ο πρωτος ουρανος κα η πρωτη γη)

are passed away (απηλθαν, went away, second aorist active indicative of απερχομα). "Fled away" (εφυγεν) in 20:11.

And the sea is no more (κα η θαλασσα ουκ εστιν ετ). The sea had given up its dead (20:13). There were great risks on the sea (18:17ff.). The old physical world is gone in this vision. It is not a picture of renovation of this earth, but of the disappearance of this earth and sky (not heaven where God dwells). It is a glorious picture here in 21:1-8 in sharp contrast to the lake of fire in 20:11-15. The symbolism in neither case is to be pressed too literally, but a stern and a glorious reality exists behind it all.