Please answer each of the following questions:
1. Who is the Alpha and Omega, and the first and the last, the Almighty in Revelations 1:8 ?
"I am the Alpha and the Omega,” says the Lord God, “who is and who was and who is to come, the Almighty.”
Since there is only one "Almighty" God...this is YHWH.
2. Who is the first and the last in Revelations 1:17-18 ?
Reasoning on the whole of Revelation, it says in Revelation 21:6-7..."Then He said to me, “It is done. I am the Alpha and the Omega, the beginning and the end. I will give to the one who thirsts from the spring of the water of life without cost. 7 He who overcomes will inherit these things, and I will be his God and he will be My son."
Jesus does not ever call his anointed ones "sons"...he calls them "Brothers". (Matthew 25:40)
This expression "First and Last" is applied to Jesus at Revelation 1:17-18. But similarly, the expression “apostle” is applied both to Jesus Christ and to certain ones of his followers. But that does not prove that they are the same person or are of equal rank, does it? (Heb. 3:1)
So the evidence points to the conclusion that the title “Alpha and Omega” applies to Almighty God, the Father, not to the Son. Jesus can be "the first and last" (ho archē kai ho telos.”) without being "Alpha and Omega". (ho alpha kai ho ō)
3. Who is the first and the last according to Isaiah 44:6 ?
"‘I am the first and I am the last, And there is no God besides Me."
In Isaiah's day, Jesus did not exist. There was no God but YHWH to Israel.
4. Now who is the Alpha and Omega, the beginning and the end, the first and the last in Revelation 22:12-13 ?
In verse 6 of Revelation 22 it says...."And he said to me, “These words are faithful and true”; and the Lord, the God of the spirits of the prophets, sent His angel to show to His bond-servants the things which must soon take place...... 12 “Behold, I am coming quickly, and My reward is with Me, to render to every man according to what he has done. 13 I am the Alpha and the Omega, the first and the last, the beginning and the end.”
This is "the God of the spirits of the prophets"...YHWH.
Jesus is never called "Almighty God" but he is the representative chosen by his Father to carry out an incredibly important mission.
6. If the risen Messiah said I have all power in heaven and in earth, is he not the Almighty?
Do you mean Matthew 28:18, where, just before he returned to heaven, Jesus said.... “All authority has been given to Me in heaven and on earth." (NASB)
Again you use a bad translation. ESV says..."All authority in heaven and on earth has been given to me."
(NLT) “I have been given all authority in heaven and on earth."
Why does Jesus need authority to be "given" to him if he is God? He had to be "given" this authority by one who had it to give....his Father.
It was prophecied in Isaiah 9:6 that the son to be born would also be the mighty God, and the everlasting Father.
YHWH said in Isaiah 43:10-12 that there was no God (el) formed before him, and neither would there be after him. (The same Hebrew word for God is used in both verses. )
Just because it has mighty before it, doesn't change anything.
I already explained Isaiah 9:6...go back and read it. There are mighty 'gods' both in heaven and on earth...but there is only one "Almighty" God....who bears a name that no one else shares. (Psalm 83:18)
John 14:28..."If you really loved me, you would be happy that I am going to the Father, who is greater than I am."
(Isaiah 10:20-21 is an example of where it calls YHWH the mighty God.)
YHWH is the 'Mighty God' spoken of here, but Isaiah spoke about only a remnant returning to the only true God in existence to them.....he is the only one who can rightfully claim the title "Almighty". Jesus was only a prophesy at that time. The man Jesus did not exist. The pre-human Jesus, who is a spirit being created by his Father certainly did. He is "the Amen, the faithful and true witness, the beginning of God's creation." (Revelation 3:14) That means he existed before anything else.