What do we spend eternity in, this flesh body or something else? The following verses explain it very plainly.
1 Corinthians 15:44 It is sown a natural body; it is raised a spiritual body. There is a natural body, and there is a spiritual body.
[We have two bodies, a natural one and a spiritual one. See 2 Corinthians 5:1-8; when we die we are present with the Lord. The spiritual body is what one spends eternity in, not their flesh/natural body. What does the word “raised” mean in 1 Corinthians 15:44? Resurrection (a transition from flesh to spirit) is what I think it means].
Ecclesiastes 12:6 Or ever the silver cord be loosed, or the golden bowl be broken, or the pitcher be broken at the fountain, or the wheel broken at the cistern.
[Ecclesiastes is written to the man under the sun, flesh man. This verse is saying when this flesh body dies for whatever the reason; see next verse].
Ecclesiastes 12:7 Then shall the dust return to the earth as it was: and the spirit shall return unto God who gave it.
[Our spirit returns to God who gave it and our flesh bodies return to the earth, we are finished with them, they have fulfilled their purposes in God's plan; they go back to the dust/dirt/soil/earth they are made of].
James 2:26 For as the body without the spirit is dead, so faith without works is dead also.
[When we die, our flesh bodies are dead without a spirit. Our spirits go back to God who gave it; see Ecclesiastes 12:7 again].
Hebrews 9:27 And as it is appointed unto men once to die, but after this the judgment:
[When this flesh body dies, and it will, our spirits go where God is and await His judgment].
This is what I choose to believe:
There is no way these flesh bodies of ours will last for ever; they get sick sometimes and they age and die eventually, they are temporary only. We have a spiritual body; that is what is meant to last an eternity, not our flesh bodies. Our spirits/souls and spiritual bodies are with God upon death of the flesh; awaiting judgment (Hebrews 9:27). I have tried to connect the dots in my own mind; (let every man be fully persuaded in his own mind).
In any case, keep studying the entire Bible my friends. Reply if you wish regardless of what you choose to believe.