After Abel was born, Adam separated from Eve. For 130 years he met with she-demons and was creating souls stemming from Abel, until they were all completed. Abel had a mixture of Good and Bad in him, with Good being prevalent, and so did all souls stemming from him. Then Adam returned to his wife Eve, and she bore Seth, who was the reincarnation of the good side of Abel.
These souls kept being rectified in mixed multitude and in Jew in Egypt for 130 years, until the rectification process was complete, and after that Moses could be born. Moses “was good”, being the reincarnation of the good side of Abel. In parallel, Amram, the father of Moses, had to separate from his wife until she was 130, to repeat Adam's separation from Eve.
Jethro was the reincarnation of Cain. His other name was Keini, because he was jealous (Kana) of the twin sister of Abel. The Gematria of “Priest of Midian” is the same as “This is Cain”. He used to get into fights like the Kohahim do and like Cain did.
The Egyptian whom Moses killed was the reincarnation of the bad part of Cain. His soul went to connect to Jethro, and this is when Jethro became complete and stopped worshipping idols. Then Jethro gave to Moses his daughter Tzipporah in marriage, thus rectifying the previous fight between Cain and Abel on account of Abel's twin sister.
Art: Titian - Cain and Abel