How do non-trinitarians reconcile Rev. 22 verses 6 and 16?

The simple answer is based on the examples the text provides both in OT and NT usage of titles. Trying to prove anything by what title God has or is given to others including Christ is a curious exercise but accomplishes little of any value.

King of Kings, Saviour, Lord, 'First and Last' is applied to both God and Jesus at different times and even other men who are not without sin.

Isaiah 44:6; 48:12 First and Last is God Rev 1:17; 2:8; 22:13 First and Last is Jesus

God the Father is called “Saviour” Is 43:11, 1 Tim 1:1; 2:3; 4:10; Tit 1:3; 2:10; 3:4; Jude 25

Jesus 1 John 4:14, Acts 5:31, Phil 3:20

Men designated as “saviour” 2 Kings 13:5; Isaiah 19:20 Obadiah 21.

We know from Isaiah and the child titled Immanuel - he wasn't God either simply because his name represented "God with us', and neither should Jesus be called God because of a title he was also given.

There are abundant plainly spoken texts that tell the truth of God and His son than trying to force a construct of unbiblical proportions on to Jesus with verses speaking of titles and names. The bible shows no special reservation for titles - they are conferred on men and God and His son at various places.

Alpha and Omega IS applied to both God and Jesus - but for different reasons.

God is obviously the beginning and the end of all things. Christ is the beginning and the end because he is the firstborn from the dead, the author and finisher of faith for a couple of examples.

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Alpha and Omega are two Greek letters! There is nothing about this we know from other texts - it's just an expression signifying uniqueness and special role. Deducing anything else is pure speculation. A cursory glance at Revelation reveals the Lamb is NOT GOD, so why would this title make ANY difference to our understanding of who Jesus is relative to his God and Father?

Answer formed from biblicalunitarian revelation-1-8

Both God and Jesus can be understood to send the angel, because Jesus is at God's right-hand (Matthew 26:64) and is God's representative - God does things through Jesus.

The NT generally, and Revelation in this case, repeatedly and clearly distinguishes between Jesus and God. Jesus is the 'Son of God', Jesus says 'My God, my God'. Jesus says 'Your God and my God'. In Revelation, Jesus (= the Lamb) is repeatedly distinguished from God, such as Revelation 1:1 "the revelation of Jesus Christ, which God gave him", Revelation 1:6 "who has made us to be a kingdom, priests to His [i.e., Jesus'] God and Father", and Revelation 3:12 which contains this distinction 4 times in one sentence. One of the verses you quote, 22:1, is another example of this ("the throne of God and of the Lamb" - two different things).

Therefore, when you have a pattern of clear statements distinguishing between the two, it is poor exegetical practice to take one, unclear instance and try to draw overarching consequences from it. Instead, the author of Revelation is repeatedly drawing a distinction between God and Jesus while simultaneously drawing a close relationship between them.

So, if we take Jesus to be saying "I am the Alpha and the Omega" and so on, then a non-trinitarian has two obvious options. First, to say that Jesus is speaking in the place of God (as his representative, much as the angel is speaking in the place of Jesus). Second, to say that all those descriptors can apply to either Jesus or God, depending on what is meant. They are all vague titles.

So whatever exactly is occurring in this passage and whatever exactly the descriptors mean and to whom they are supposed to be applied, what is clear from Revelation overall is that Jesus (= the Lamb) and God are two distinct things.