Rev.1:5 – and from Jesus Christ, the faithful witness, the firstborn of the dead, and the ruler of the kings of the earth. To Him who loves us and released us from our sins by His blood —
John saw a resurrected man on the beach of the Isle of Patmos. Jesus was not a vision or a spirit, He came to John bodily and physically. That in itself has huge implications. First, the Creator, God Himself, was standing in front of John as a human. God became a man for all time. He died for us and is ministering as a priest for us before the Father in heaven. Here, Jesus is saying that He was the first man to raise permanently from the dead. Several others had been raised from the dead throughout history only to die again and go back into the grave. Jesus was raised in a new incorruptible body. He was the first of an entire race who will experience this. His body is an eternal, immortal body. Someday I too will have one. Here is how Adam Clarke describes this.
“The beginning, the first-born from the dead. In 1 Corinthians xv. 20, Christ is called the first-fruits of them that slept; and here, the chief and first-born from the dead; he being the first that ever resumed the natural life, with the employment of all its functions, never more to enter the empire of death, after having died a natural death, and in such circumstances as precluded the possibility of deception. The arch, chief, head, or first, answers in this verse to the first-fruits, Jesus Christ is not only the first who rose from the dead to die no more, but he is the first-fruits of human beings; for as surely as the first-fruits were an indication and pledge of the harvest, so surely was the resurrection of Christ the proof that all mankind should have a resurrection from the dead.”
For John this could be personal. John was in exile and all of the other apostles had been martyred (or would be shortly). Jesus was telling him, as well as us, that the final and greatest enemy, death itself, had been totally defeated by the death and resurrection of Jesus Christ. As the book of Revelation unfolds we see the final scene of the great plan of God. The dead will be raised, we will be given new bodies like His, we will be comforted by Christ, and will rule with Him for eternity.