Many key NT concepts were created during the latter part of the Second Temple period, namely the 3rd and 2nd centuries BCE. This includes the creation of a spirit world, the invention of evil spirit beings, a war in heaven, invention of demons, and such. So read books such as 1 Enoch and Jubilees at the very least. Remember that the Book of Daniel was written in the 2nd century in the wake of this eschatological phenomenon.
Do not try to blur the Bible books into a homogeneous entity, Each writing was created within its own cultural context for its own immediate community's needs. For example, the Book of Job was written to explain why God's chosen nation was always being punished. In other words, climb into the Jewish mind of each period. Judaism experienced several metamorphoses.
Doug