v1: As with all things, the river of the water of life flows from God and the Lamb; its origin is divine and eternal. Here is the fulfilment of God's promise to grant access to this water, 21.6. There is an echo here of Eden, with rivers, and the tree of life, Gen 2.9-10.
v2: The curse of Babel is finally removed; all are truly one in Christ; 21.24 refers to the nations of those who are saved; see also 7.9 where representatives of all nations appear in Heaven. There is health (shalom) for all nations in eternity.
v3: The curse of sin is removed; this was taken away when Christ died; there is no fear of judgment.
v4: Only now will men see the face of God; Ex 33.20, for we shall be like Christ, 1 John 3.2.
v5: There is no need of anything, as in 21.23; for all our needs are met in God. There is no longer any enmity, so we don't think of God's people as reigning over others; but rather enjoying the dignity and status of sons of God.
v6: The angel who revealed the Revelation to the servants of God (1.1); all that John has seen will happen, for the words are trustworthy and true. The message is from God, and will surely be fulfilled.
v7-21: The epilogue brings the challenge, "I am coming quickly," and, like the gospel writers especially, the motivation is that we make sure we are ready.
v7-9: Obedience; the challenge of the will. Although John saw and heard wonderful things, the blessing of God is for all who obey what has been revealed; hearing and seeing must be followed by our obedience. Some things are not right for the Christian, and even John is rebuked here, see also 19.10. Obedience begins with our worship of God.
v10-11: These truths remain relevant. There is something in man which continues his rebellion against God. Many, who started in sin, continue. And many who live righteously continue to do so. Most people behave according to their character most of the time.
v12-15: Reward; the challenge of the intellect. There is a reward for believers, distinct from salvation by works, but reward for works. Christ declares His own divine Names; He was at the beginning of all things, and is eternal.
Outside are unbelievers (21.8), who prefer sins, rejecting God and Christ. Again, murderers and immoral are listed with liars, see 21.8.
v16: The Lord Jesus Himself brings the testimony for His churches. The 'you' here is plural, indicating the responsibility of all His people to take His message.
17-20: Fellowship; the challenge of the emotions.
v17: The invitation to enter into fellowship with God; the invitation is from the Spirit (in us) and from the bride (in Heaven). The invitation, which is repeated (v1; 21.6) is to take freely of the water of life; we will enjoy the fullness of God in Christ.
v18-19: The final warning to the ungodly, to those who seek to modify the word of God, by adding or subtracting; this is a serious matter, such that God will add to him the plagues recorded therein, or exclude him from its blessings. The godly man believes it entirely, Ps 119.160, even if he struggles to understand all of it.
v20: The one who speaks (v16), who sent His angel (v6) is the one who is coming soon (v7); His words are faithful and true; and thus His final wonderful promise is also true. In response the faithful believer simply prays, "Amen. Come, Lord Jesus."
v21: In the meantime, while we await His return, we enjoy His grace, and we have all we need.