You asked, how does the story of Elijah and Enoch fit with what Jesus said in John 3:13 which is, along with the two preceeding verses: "Verily, verily, I say unto thee, we speak that we do know, and testify that we have seen; and ye receive not our witness. If I have told you earthly things, and ye believed not, how shall ye believe, if I tell you of heavenly things? And no man hath ascended up to heaven, but He that came down from heaven, and even the Son of man which is in heaven."
I know it's long but this is how I've come to understand it.... I hope it makes sense to you. :)
The Bible says, "Enoch walked with God: and he was not, for God took him." (Gen 5:24) Also, Hebrews 11:5 records: "By faith Enoch was translated that he should not see death; and was not found, because God had translated him: for before his translation he had this testimony, that he pleased God."
We need to not forget that nobody who doubts can understand God's Word (which I'm still learning.) It is by faith that we understand. The only way we can hope to see the picture of it all, through all the seeming contradictions and difficulties... is in maintaining complete confidence in it's Author. Part of it is that we have to keep in mind that God is the first, the last and the same forever. He cannot lie and therefore His word cannot be a contradiction. The Bible doesn't need harmonising, it is in perfect harmony with each and every other verse. It's just our part to recognize this harmony. (Which I can't boast of.) If we try and make it harmonise, we make a sad muddle, because in trying we believe show unbelief in it's perfectness.
When I was little, Mum would read us the gospels for storytime. I remember her once reading about Jesus promise to the disciples (and us) that if we had faith like a mustard seed, we could move mountains. I wondered at the time why the disciples didn't just try. Why didn't they test it out? Then I came to realize that that would've been unbelief, not really believing it, but almost taking it as a challenge.
Back on the subject. :) The truth is that Enoch was translated and taken to Heaven without seeing death, a thing that is only recorded of one other man - Elijah. Most men (and women) no matter how good die, and stay in the grave waiting for the resurrection to raise them up, (as is the case with David, "he is both dead and buried" and his grave remains today. Acts 2:29) When the Lord comes all the dead in Christ will be raised to immortality and the living will be translated like Enoch changed in a moment, in the twinkling of an eye, and be caught up to "ever be with our Lord." 1 Thess 4:15-17; 1 Cor 15: 51, 52
We're left with the remaining question, how do we understand John 3:13 in the light of the fact that Enoch was taken to be with God - who's throne is in Heaven? The question answers itself when we look at the rest of what Jesus was saying. He was talking to Nicodemus about new birth or sonship. "Except ye be born of above, ye cannot see the kingdom of God," verse 3 margin. Jesus was born from above when He came into this world, but other men have to be born again, as our first birth is of the earth. And when they are born again, from above, then their citiczenship is of heaven, and they walk and dwell with God. "Even when we were dead in sins, hath quickened us together with Christ, (by grace ye are saved;) And hath raised us up together, and made us sit together in heavenly places in Christ Jesus." Ephesian 2:5,6 Such can ascend to heaven like Enoch and Elijah; even as the saints will when Jesus comes again.
Jesus said, "No man hath ascended up to heaven, but he that came down from heaven, even the Son of man which is in heaven." Jesus was in heaven (like we are in Heavenly places on earth) even while he was on earth. Even so it must have been with Enoch, for "he walked with God." He was born from above, and when he talked to other people about heavenly things, he shared what he knew, and told of things he had seen, just as Jesus had.
So it may and should be today. By His Holy Spirit - the Spirit of adoption, whereby we cry, Father; we are made to know the 'deep things of God." 1 Cor 2:10 " The secret of the LORD is with them that fear him." Psalms 25:14a. "But the natural man receiveth not the things of the Spirit of God; for they are foolishness unto him; neither can he know them, because they are spiritually discerned." So the Christian may talk of solemn and joyous realities which he has seen with his Father, and to those who listen he may seem to be raving. He has been in communion with God in the heavens, and he speaks what he knows, and testifies what he is seen. "What he hath seen and heard, that he testifieth, and no man receiveth his testimony." Only the Spirit of God can enable a man to discern heavenly things when they are spoken.
I know this all seems too much to be true of man, but remember that Christ's spoke of Himself in this connection, as He always did as the Son of man. He identified Himself with men in order that men might for ever be identified with Him. By Him we have access to God, being made partakers of the Divine nature. We have "boldness to enter into the holiest by the blood of Jesus" (Heb. 10:19), because in Christ we come down from heaven. By Him, and Him only we enter Heaven. Since we become sons of God by putting on the Lord Jesus Christ, it is true that there is only "one new Man," namely Christ Jesus, so that even when all the saints shall have been taken to heaven, it will still be true that no man hath ascended to heaven but the Son of man. (John 15:4 Jesus says that we are in Him and He in us, so we are that closely identified together, that it is Jesus.) And since all this is true of us, we can see that the redemption of our body for which we wait is a natural consequence of our birth from above, and we know that we shall soon be taken bodily to be ever with the Lord.
Also, to do with angels being immortal, I found this verse in the Bible. It seems I'd never seen it before. When I found it it was like, 'Wow!'
"Which in His times He shall show, who is the blessed and only Potentate, the King of kings, and Lord of lords; who only hath immortality." 1 Timothy 6:15, 16.
Also, with Isaiah 14 and Ezekiel 28, talking about two different people at once, I think Psalms 72 is interesting in connection. It's a psalm of David's to Solomon, his son - but who else do you think he's talking about aswell?
I guess this is getting really long now, so I won't add anything more to it.
But I love you, Maggles!
P.S. You might have to read over it twice to get what I'm trying to say, I found it to be something that really roused my thinking.