 The underlying theme of the "Tanna debe Eliyahu", which (with many interruptions) runs through the whole work, is the evolution of the world-system.The midrash calls the single periods of the history of man ""shittot"" (series).The first series, which deals with the beginning of the world and extends to the moment when man was driven out of Eden, consists of two subsections, (a) ""Ma'aseh Merkabah"" and (b) ""Ma'aseh Bereshit"."