I concede that in verse 9, Jesus refers to the incident as a vision.
Strongs Concordance: 3705 "from 3708 something gazed at, i.e. a spectacle (esp. supernatural): sight, vision."
3708 "prop. to stare at(comp. 3700), i.e. (by impl.) to discern clearly----"
3700 "to gaze(i.e. with wide open eyes as at something remarkable----"
I know that we must be careful when using a concordance to not apply all the possible meanings listed to any given passage. We need to discern from context. However it is also true that we should check to make sure we are not considering only our modern day interpretation of a word.
Even if we in this incidence land on "esp, supernatural", that does not mean it wasn't real. Even if real, it was supernatural. The definite phrasing of the event , that Moses and Elijah appeared and were talking to a transfigured Jesus etc. suggests to me that they were really there.
I'm not relying on the modern definition of vision. As I stated, Peter indicates that it was the second coming of Christ.
16 For we have not followed cunningly devised fables, when we made known unto you the power and coming of our Lord Jesus Christ, but were eyewitnesses of his majesty.
17 For he received from God the Father honour and glory, when there came such a voice to him from the excellent glory, This is my beloved Son, in whom I am well pleased.
18 And this voice which came from heaven we heard, when we were with him in the holy mount. (2 Pet. 1:16-18 KJV)
Long after Jesus' crucifixion Peter refers to this event as the power and coming of the Lord Jesus Christ. We know that His first coming wasn't in power. We know that His second one will be. Jesus was alive when the event took place. How could it have been His literal second coming when He was still hadn't departed the first?
We're also told that Moses and Elijah appeared with Jesus in glory. What does that mean, in glory?
40 There are also celestial bodies, and bodies terrestrial: but the glory of the celestial is one, and the glory of the terrestrial is another.
41 There is one glory of the sun, and another glory of the moon, and another glory of the stars: for one star differeth from another star in glory.
42
So also is the resurrection of the dead. It is sown in corruption; it is raised in incorruption:
43 It is sown in dishonour;
it is raised in glory: it is sown in weakness; it is raised in power:
44 It is sown a natural body; it is raised a spiritual body. There is a natural body, and there is a spiritual body. (1 Cor. 15:40-44 KJV)
So here, according to Paul the body is resurrected, in glory. Moses and Elijah appeared with Jesus in glory. They appeared resurrected. Paul also said that Jesus was the first born from the dead.
But now is Christ risen from the dead, and become the firstfruits of them that slept. (1 Cor. 15:20 KJV)
Jesus too tells us this,
5 And from Jesus Christ, who is the faithful witness, and the first begotten of the dead, and the prince of the kings of the earth. Unto him that loved us, and washed us from our sins in his own blood, (Rev. 1:5 KJV)
If Jesus is the first born of the dead, how can Moses and Elijah have been resurrected before Jesus died? They couldn't have. The only thing that makes sense is that it was a vision just as Jesus said it was. Yes, Peter, James, and John, saw it. Was it really the resurrected Moses and Elijah? I couldn't have been.
You see, the reason these appear to be alive to you is based on the presuppositions you bring to the text. I know, there was a time when I would have made the same arguments you are making. However, I've changed my presuppositions. That's where the title of this thread comes from. "What is a man" I used to believe that man was a soul and/or spirit that lived in a flesh body and continued on after death. However, upon closer scrutiny and more in depth study of the Scriptures I've since come to understand that that is not what a man is. The presupposition of what a man is changes how one sees these passages.
To claim that the dead live on after death one must first establish that a man can live apart from the body. I don't believe one could do that from Scripture.