1 Thessalonians 5:23 "And the very God of peace sanctify you wholly; and I pray God your whole spirit, soul and body be preserved blameless unto the coming of our Lord Jesus Christ."
Here we are plainly described as having three parts, body, soul and spirit.
Revelation 20:4 " And I saw thrones, and they sat upon them, and judgement was given unto them: and I saw the souls of them that were beheaded for the witness of Jesus....."
If someone is beheaded, their body must surely be dead. John saw the souls of those who were dead. If the souls aren't immortal, then how is it John saw them?