The definition of Utopia is a state in which everything is perfect, and we see this in Revelation 21. We see “a new heaven and a new earth,” taken from Isaiah 65:17-18 in the context of Jerusalem. Here at the end of Revelation, we find the new Jerusalem coming down out of heaven from God.
The reference to no sea is interestingly specific and could relate to its previous defeat, with its link to the beast, evil, and/or Rome. Other Jewish writing also saw this demise of the sea. We also saw that the sea was heavily linked to Rome trade and its success. Without the sea there would be no trade, merchants, sea captains, wealth, or corruption, but rather God would supply to all the needs of new Jerusalem.
But this Holy city is more than a city, it's described as a bride. We see elsewhere in the New Testament that God's people, (the church), are described as Christ's bride. We've even seen earlier God's people dressed in white linen, similar to a bride, signifying their purity. God will live with His people. It will be a temple city (just like old Jeruselum), but the temple will be the Lord God Almighty and the Lamb. There will be no need to make sacrifices and we will be with our God, confirming that the faithful witness has gone to all nations.
“Many nations will be joined with the Lord in that day and will become my people. I will live among you and you will know that the Lord Almighty has sent me to you. (Zechariah 2:11)
The old order has gone and there will be an end of sorrow. No more death and mourning, no more crying and pain. This will be in direct contrast to the fate that are not God's people. They will experience the 2nd death.
The words "It is done" echos those of Christ on the cross,
When he had received the drink, Jesus said, “It is finished.” With that, he bowed his head and gave up his spirit. (John 19:30)
Quickly followed is a reminder that He is the Alpha and the Omega, the Beginning and the End. He is sovereign over all and He will accomplish all that He has promised.
From verse 9 we see the attention move to the materials and the magnitude of the new Jerusalem. Are these literal dimensions? Unlikely! These are purely to convey the glory of God that will exist. Isaiah 54:12 talks of the future glory of Zion having walls made of precious stones, (see Exodus 28:17-20). Could the gates of pearl reference the parable in Matthew 13:45-46?
The city has walls to show its grandeur. No city of any worth doesn't have a city wall. The book of Nehemiah shows us the importance of a city wall. In the case of new Jeruselum, it isn't for protection because it tells us the gates are always open. Cities closed their gates at night for protection, but we're told that there will be no night and God will protect us, God fears no one. In fact, there will be no sun or moon. God's glory will provide the light.
This is the message we have heard from him and declare to you: God is light; in him there is no darkness at all. (1 John 1:5)
New Jerusalem is God's creation, mirroring what we find at the beginning of the bible with the Garden of Eden, completing the journey of salvation found throughout scripture. Christ's bride shows us we are loved. Through salvation and love, we are able to find comfort, whatever our situation might be. When our hardships are too much, we are to lift our eyes to the new heaven and the new earth, where we will live with God, forever and ever.