Revelation 1:17 - When I saw him, I fell at his feet like a dead man. He laid his right hand on me, saying, "Don't be afraid. I am the first and the last,
Revelation 1:18 - and the Living one. I was dead, and behold, I am alive forevermore. -- World English Bible translation
The thought trinitarians would like to read into this evidently is that when Jesus refers to himself as "the first and the last" that this somehow means that Jesus is Jehovah, who says in Isaiah 44:6: "I am the first, and I am the last." Additionally, the assumption is made that Jesus' reference to himself as "the first and the last" means that Jesus is, has always been and always will be.
What does Jesus himself indicate regarding his reference to himself? Did he say he has always been -- that he was uncreated, and that he could never cease to exist? No, he, as the first and the last, plainly says: "I was dead." Thus he is telling us of a time when he was not. By such Jesus is, in effect, denying that he is Jehovah, who cannot die. But Jesus says, in reference to his being brought out of the death condition, "I am alive forevermore."
This is reiterated in Revelation 2:8 where Jesus refers to himself as: "The first and the last, who was dead, and has come to life." For him to come to life would mean that he, the first and the last, had no life while dead. If he was actually alive while dead then he never was actually dead.
Of course, our trinitarian neighbors would tear what Jesus said apart and have the expression "the first and the last" apply to the the alleged "God" nature of Jesus while they would separate the expression "who was dead" as not meaning "God" whom they allege Jesus is claiming to be in the expression "the first and the last", but rather only the body/flesh/humanity of Jesus. The First and the Last, they claim is God, who did not die, but rather it was the "man" Jesus who died. In effect, they would end up denying what Jesus actually said, that 'the first and the last' was indeed dead. In reality, there is no reason to divide this up so, except to satisfy the added on trinitarian concepts. It was Jesus himself who died, ceased to have sentiency, and it was Jesus himself who came back to life.
The contextual evidence is that Jesus is speaking about his being the first and last in some way concerning his being dead and brought back to life. How could this be?
Revelation 1:5 refers to Jesus as the "firstborn" of the dead. No one had been brought back to life directly by Jehovah never to die again, except Jesus. Jesus was the first. At the time of the writing of the Revelation, Jesus was also the last that had been actually brought back to life, never to die again, and he is certainly the last firstborn to be made alive. There will never be another firstborn from the dead. Believers are now "counted" or "reckoned" as justified and alive, but are not actually raised to life until the "last day" -- the day of the world's judgment. Jesus was also the "last" to be directly brought back to life by Jehovah, since God has given the authority of the resurrection and judgment to Jesus. -- John 5:19-30; 6:39,40,44,54; 11:24; 12:47,48; Acts 17:31.
Jehovah, of course, is the first and last EL/ELOHIM (strength, power, might) in the universe. (Isaiah 44:6) No one can have any power or might aside from him. Even the demons have to depend on Jehovah for any power they have (which power they misuse). They have no power (strength, might) of their own, except that they have received such power from God. Jehovah, the God and Father of Jesus, is the only ultimate Supreme Being. Additionally, none of the idol-gods of men were formed before Him, since He had no beginning of existence, nor can any be formed after Him, since he has no ending of existence.
What we do not find in these verses is any thing that says that Jesus is a person of the Most High, or three persons in one God. The idea of "trinity" or that Jesus is Jehovah has to be imagined, assumed, added and placed over the scriptures in order to make the scriptures seem to support those ideas.
For more concerning this, see: