Cofty: I think I am right in saying that the dualistic idea of a devil was adopted from Zoroastrianism during the exile.
That's the logical conclusion. As a concept it does not seem evident in writings that have a pre-exilic background, but afterwards, as for example, in the Qumran (Dead Sea) scrolls, it is. An example occurs in Vermes' translation of the DDS, ( 1QS 3:17-25) where the author speaks of having to choose between being led by either the Angel of Darkness or the Angel of Truth.
The Christian concept of heaven and hell has also been attributed to influences of Zorastianism by some Biblical scholars.
In Zoroastian thought, the bridge between heaven (paradise) and hell was seen as the fine edge of a sword. Difficult to walk upon and hard to balance.