It is sad today that many Christians don't understand this from Scripture, especially since those who had 'faith' in Old Testament times did know.
     Apparently, that's why so many fellow Christians are lacking in their understanding about what 'Heaven' is going to be like in the future. Ask them; you'll get all sorts of concoctions. Many can seem to dream up all kinds of cotton candy visions of Heaven, living in a cotton-like ether space of floating clouds and such, and nothing else below. GOD created this ancient earth to be inhabited, and that's just the way it's going to be put back in His Eternity also, (God’s Plan) as it was before Lucifer rebelled.

 

Isa.45:18: For thus saith the Lord That created the heavens; God Himself That formed the earth and made it; He hath established it, He created it not in vain, He formed it to be inhabited: I am the Lord; and there is none else.

 

 Isa.14: Read All.

 

Ezek.28 & 31: Read All.

 

 This 'flesh age' is a TEST to see who we would worship, and nothing more. That's why we don't remember that first time 'of old', because it would influence our decision of who we would worship today. Lucifer's rebellion caused this 'flesh age', and he has been given control of it. There never was any such thing as 'death in the flesh' during that first time of old, because none of us were in flesh then; we were all 'spiritual bodies', as it will be again in the future Eternity.

 

 That's why Paul is talking about the re-establishing of that original spiritual first earth age of God's Holy City with, "...flesh and blood cannot inherit the Kingdom of God..."

 

I Cor.15:50: Now this I say, brethren, that flesh and blood cannot inherit the kingdom of God; neither doth corruption inherit incorruption.

 

 Since Jesus Christ came as Saviour, how did He accomplish It? He came in the flesh, being born of woman just like you and I, but He was perfect even while in the flesh, which was required to defeat Satan who is 'Death'

 

Heb.2:14:  Forasmuch as the children are partakers of flesh and blood, He also Himself likewise took part of the same; that through death he might destroy him that had the power of death, that is, the devil;

       So if you understand all of this, then know that we, who believe on and accept Jesus Christ as our Salvation, AND by refusing to worship the 'false messiah' who comes first, our souls will have already had 'eternal life', beginning at that time 'of old', i.e. the first earth age before Lucifer rebelled, all the way through this flesh age, and even evermore in the last earth age to come, GOD's Eternity. That is the 'first resurrection' written in. Those who refuse Salvation through Christ today; they are the 'spiritually dead', also written of in Those spiritually dead 'live not again' during the thousand year reign of Christ and His elect,..

 

Revelation 20: Read All:

 

Revelation 20:5. But the rest of the dead lived not again until the thousand years were finished, This is the first resurrection.

 

... In the eternal everlasting 'sense' of the spiritual body, because their 'image' can still yet perish because their spiritual body is still 'mortal' at that point.