During the Intertestamental Period, the concept of Sheol begins to expand. The first thing worth mentioning is that the Greek word for the place of the dead, hades, becomes another name for Sheol. Greek and Hellenistic thought not only influence the change of name association, but also the concept of what Sheol/Hades is like. The concept of an intermediate state where the souls of the dead are conscious is prevalent in the Greek portrayal of the afterlife. The Jews of the day absorbed this belief, as well as the notion of having different "compartments" in Hades to divide the wicked dead from the righteous dead. Thus, Sheol is now seen as an intermediate holding place for the dead, while they await the resurrection (this view of resurrection was held by the Pharisees, but not the Sadducees).
The book of 1 Enoch gives us insight to this development,
At that moment, Rafael, one of the holy angels who was with me, responded to me; and he said to me "These beautiful corners (are here) in order that the spirits of the souls of the dead should assemble into them- they are created so that the souls of the children of the people should gather here...I saw the spirits of the children of the people who were dead, and their voices were reaching into heaven until this very moment (and making suit) ...and he replied and said to me, "These three have been made in order that the spirits of the dead might be separated. And...the souls of the righteous have been separated. 1 Enoch 22:3-9