1. Then I saw a new heaven and a new earth; for the first heaven and the first earth had passed away, and the sea was no more.
The phrase “Then I saw a new heaven and a new earth” reveals that the new earth will be without sin and God the Father and God the Son will live with men for all eternity.
The phrase “for the first heaven and the first earth had passed away” details how it will happen which is found in 2 Peter 3:10 which says, But the day of the Lord will come like a thief, in which the heavens will pass away with a roar and the elements will be destroyed with intense heat, and the earth and its works will be burned up. NASB
2 I also saw the holy city, the new Jerusalem, coming down out of heaven from God, prepared like a bride adorned for her husband.
The holy city, the new Jerusalem is where God Himself is going to live [Revelation 21:22-26] once it is placed on the new earth.
3 Then I heard a loud voice from the throne: Look, God’s dwelling is with humanity, and he will live with them. They will be his peoples, and God himself will be with them and will be their God.
An announcement will be pronounced in heaven that God’s purpose since the beginning of creation will take place, to live with us. The reason why God, after the new earth is created, will live with men is that sin will be eradicated.
4 He will wipe away every tear from their eyes. Death will be no more; grief, crying, and pain will be no more, because the previous things have passed away.
With our new body [spiritual body 1 Corinthians 15:44] which will be without sin, we will experience unimaginable joy for all eternity. The nature of sin [envy, deceit, selfishness, the love of money/material, murder, evil intentions, lust, the worship of idols, and death] will end once and for all.
1 Corinthians 15:54-57
54 When this corruptible body is clothed with incorruptibility, and this mortal body is clothed with immortality, then the saying that is written will take place:
Death has been swallowed up in victory.
55 Where, death, is your victory? Where, death, is your sting?
56 The sting of death is sin, and the power of sin is the law. 57 But thanks be to God, who gives us the victory through our Lord Jesus Christ!
5 Then the one seated on the throne said, “Look, I am making everything new.” He also said, “Write, because these words are faithful and true.”
The phrase “Then the one seated on the throne” Is in reference to Jesus Christ [compare John 12:39-41 to Isaiah 6:1-10]
The phrase “these words are faithful and true.” Shows that Jesus Himself testifies to the reliability of the Word of God.