It has been said by some that the words: “Write, for these things are true and faithful” (Revelation 21:5), were spoken, not by Christ, but by an angel. This might be true, but it seems awfully clumsy to have Christ speaking at the beginning of Revelation 21:5, but then an angel concludes the verse, but then Christ speaks again in the next verse. All this occurs without John ever mentioning an angel had spoken between Christ’s two declarations. It is easier to believe that Christ is speaking to John throughout the discourse, until John begins to describe his surroundings in Revelation 21:8.
The speaker in Revelation 21:6 identifies himself as the Alpha and the Omega. This is the glorified Jesus, and we know this from the other references to his being the Alpha and the Omega in other verses found in the Apocalypse: Revelation 1:8, 11 and Revelation 22:13.
In Revelation 1:8 the text says: “I am Alpha and Omega, the beginning and the ending, says the Lord,” and in Revelation 1:11 John heard a voice behind him saying: “I am Alpha and Omega, the first and the last…” and when John turned to see who that was, he saw Christ standing among the seven lampstands (Revelation 1:13). Revelation 21:6 quotes Revelation 1:8 verbatim, which causes some to conclude the speaker in Revelation 1:8 is different from he who spoke in Revelation 1:11. In other words the Father is the speaker in verse 8, while Jesus spoke in verse 11. This is not so, however, and we know this by reading Revelation 22:13. There the speaker includes all three clauses: Alpha and Omega, Beginning and the End, First and the Last. We know this is Jesus ,because of what the same speaker says in the previous verse: “behold, I come quickly; and my reward is with me…” and again in verse 16: “I, Jesus, have sent mine messenger (John) to testify unto you …” (parenthesis mine). Therefore, the speaker is Christ throughout the discourse (Revelation 21:5-8).
So, having identified the speaker as the glorified Jesus, what did he say, and what does this mean? The Lord told John: “It is done… I will give unto him that is athirst of the fountain of the water of life freely” (Revelation 21:6).
First of all, Jesus told John it is done! The same words appear in Revelation 16:17 with the pouring out of the seventh vial, which was the destruction of Babylon or the destruction of Jerusalem and the Temple. Jesus’ words here: “It is done” are quite different from what he said on the cross: “It is finished!” (John 19:30), although in English they seem very similar, if not the same. In the Greek it is teleo (G5055), meaning “finished, bring to a close, fulfill” (John 19:3). In Revelation 21:6 and 16:17 the Greek word is ginomai (G1096), and it means “to become, i.e. to come into existence, begin to be.” In other words, what was brought into existence, or at least established as **the** authority was the New Covenant. This was done, as the Old Covenant passed out of existence (Revelation 16:17) with the destruction of Babylon / Jerusalem and its Temple. Thus, it is further proved that the millennium is not a literal thousand years. How could it be, if the New Covenant was brought into existence or established as **the** authority thousands of years after Christ was crucified? The futurists are wrong, because their eschatology makes no sense. It is as though they claim: “Are you going to believe me or your lying eyes!” In other words, futurists deny the obvious.
Next, Jesus says: “I will give unto him that is athirst of the fountain of the water of life freely” (Revelation 21:6). This has to do with receiving the truth of God rather than trying to live off the doctrines of men (cp. Jeremiah 2:13). We have been raised from the dead, spiritual death, and have come to know God (Ephesians 2:1-5 and compare 1Corinthians 2:6-14). Jesus claimed in John 7:37-38, “If any man thirst, let him come unto me, and drink. He that believes on me, as the Scripture says, out of his belly shall flow rivers of living water.” This is what the Scripture speaks of in Joel 3:18. Jesus is that Spring or Fountain of Living Waters! It is not a physical matter. The new creation is a spiritual creation.
 See Thayer’s Greek Lexicon for both teleo (G5055) and ginomai (G1096).
 A line delivered by Chico Marx in the film Duck Soup.