מוסר אויף שופטים 1:16

Cain and Abel were the first men born by woman. They were intended to be the typical "אדם" i.e. representative of what mankind should develop into. Now it had become the turn of the people of Israel to be refined and to acquire the appellation "Adam." According to our Kabbalists, Moses was the re-incarnation of Abel, הבל, whereas Yitro was the re-incarnation of Cain, חבר הקיני (see Judges 1,16, Zohar 3,216).