"Take our lives and let them be, consecrated Lord to Thee ..."
I'm not sure where the idea of an immortal soul came from. The earliest is probably Egyptian (but did this apply to peasants, or was it just the pharaohs and their escorts?) Certainly by Greek times it had become very popular with whole books of myths being written about Hades, Cerberus, the River Sychs and others. By Viking times the idea was that any warrior who died with a sword in his hand could enter Valhalla. We read of these past beliefs thinking how silly they are in today's world. But has it changed that much?
The idea that we do not die, but that something lives on is wishful thinking (possibly – unless they also believe in eternal punishment in hell - which is another topic for discussion at another time!).
The Bible is very straight forward in this idea; "The soul that sinneth shall die". You can't get any more straight forward than that. And all have sinned, so all deserve to die.
This is also central to Jesus' sacrifice. He died! Then God raised him on the third day. If he didn't die, what was the point in resurrection?
What happens to our bodies when we die?
What happens to our spirit when we die?
Why is the idea of an immortal soul so popular?
Was Adam immortal in the Garden of Eden?