I've already explained what death means in the Bible in at least a few posts a while back. I will repost some of it here:
Death does not equal non-existent. Death means separation in the Bible. The Bible speaks of different kinds of death. I've posted on the kinds of death before. We are all spiritually dead before we get saved. Does that mean we were non-existent before we were saved?
Everyone does not have an immortal soul so we do not need to prove anything to you here. Immortal in the Bible means living forever. Everyone does not receive a glorified body at their resurrection either. Only the saved will put on immortality. Only the saved will receive glorified bodies. Those who die without Christ will die in their sins. They will die what is called in the Bible the second death. The unsaved at their resurrection will be resurrected to an eternal death. They will die forever with an eternal body and soul forever being separated from God. One type of body will live forever; the other type of body will die forever. That's a big difference. https://www.curezone.org/forums/fm.asp?i=2364382#i
Also, regarding the verse that says that the spirit goes back to God when we die physically, I am finding more information on that. I am now thinking that this verse means for all even the unsaved, but their spirit may no longer belong to them. It may be that only the soul of the unsaved goes to hell and after the white throne judgement the unsaved get some sort of a body that will last forever that will be cast into the Lake of Fire. The Bible is not clear on how all of this works, but I definitely don't believe like Vekky and High on Water. I'm just not sure on the correct interpretation of this verse:
"Then shall the dust return to the earth as it was: and the spirit shall return unto God who gave it.
Ecclesiastes 12:7 King James Version (KJV)
Remember the Bible is clear that we are spirit, soul, and body.