The monotheistic religions cannot be sustained without the satan, and that’s because in their development towards monotheistic they faced a big problem.
To understand this problem lets go back to the beginning when there was many gods and goddesses and each have specialized power.
One come and say these are many gods lets reduce them to just two gods one for good and other for evil.
so after that , when it was time for monotheistic, the writer faced this problem, how to get rid of the evil god and make it only one god, the good god. Because the role of the gods at that time is to bring victory to the king, and If a king have good god, then the other king have to be with evil god.
So he converted the evil god into satan, but while he writing the book, back in his head he know the satan is god of evil, this entered him through left brain and right brain conflict.
Sometimes he write with left brain try to make satan "the highest of all the angels a fallen angel ", but his right brain knows that satan is god, the result was very wired; a good god - who suppose that he created everything - making bet with Satan ,challenge satan , argue with satan. And compete with him on human.
I think one of the disastrous thing happen to mankind is the making out the god and satan, because it give the authority to do every things, millions slaughtered, burned, tortured to death, because of this division “god and satan” “if you are not with me then you are with the satan”!!!.