Continuing with Akenson I found more data re sources of the idea of immortality. I added it to the website at
larry.1afm.com, then posted the article on the website. (Better to go first to the website, then select supplements, then names, then immortality, or you may read it here.)
During most Old Testament times Israel lacked any definite concept of immortality. The word Sheol, generally used of the dead, most often simply means the grave. (In a few places like Job 19:26 we perceive some intimations of an afterlife; but the author of Job, according to many modern scholars, lived quite close to New Testament days, although many have disputed that.)
However Isaiah prophesied that in time the Lord would swallow up Death, and Paul used this passage as a source for his great chapter on Resurrection..
Daniel, thought to be written in the 2nd century B.C., provides the definitive statement of Resurrection and Immortality at Daniel 12, which appears to be a prime source of the statement attributed to Jesus in Matthew 25.
Akenson, pages 24-9, in a fascinating description of the book, 4 Maccabees (ca 167 BCE), gives us another significant precursor of the immortality of the individual soul.
(See also Riley, Chapter 6 of The River of God.)