The curse is now revoked so that mankind can take hold of the fruit of the tree of life and live forever. The throne of God and of the Lamb is not remote in heaven but on earth in the New Jerusalem, God's dwelling place is with man, heaven has moved to the earth. There will be plenty to do in heaven, 'his servants will serve him'. They will not need the light of a lamp or the light of the sun, for the Lord God will give them light. And they will reign for ever and ever.
Night is abolished because it is associated with evil, light is associated with that which is good.
Compare those who reign for ever and ever with the fate of those who follow the beast and who are tormented day and night for ever. The Lord, the God of the spirits of the prophets, sent his angel to show his servants the things that must soon take place. Soon means in the biblical sense of 'I am coming soon'. This picture of heaven is true, it can be trusted, it is worth dying for.