People who go so far as to deny that the soul is immortal can never philosophically explain how a "pile of chemicals" or "molecules in motion" manage to cohere together in what we call "a living being". They can't create even the smallest speck of life.
But more importantly, they can't explain how man can understand things that are immaterial -- such as justice, truth, fairness, goodness, and why men all seem to desire to live forever.
Either we ARE going to live forever, or they're denying God's goodness by claiming that He gave ALL His beings a longing that will never be fulfilled.
Why would a pile of chemicals be able to transcend the physical world in any way? One cannot escape his own plane of existence. If we weren't half in the spiritual realm, we would have no concept of spiritual things.
It's been a while since I learned this stuff, so I'm a bit rusty at explaining it.
Matthew