Q. I have two questions about the beginning of history. What did Adam and Eve really do wrong when they ate the fruit of the tree? What was the cause of the quarrel between Cain and Abel?A. According to Nachmanides (Ramban), before eating the fruit of the Tree of the Knowledge of Good and Evil, Adam and Eve lacked the power to make decisions. Like the heavenly bodies, they were like mere machines, programmed to function in a set way.
By partaking of the fruit of the tree, their destiny changed for ever. They gained the power of decision-making and were now able to choose their path, whether moral or immoral. This therefore provides an origin for human free will.
The root of the quarrel between Cain and Abel in Genesis chapter 4:9 is not completely spelt out in the text.
The Italian commentator Umberto Cassuto suggested that it harks back to verse 2, which says, “Abel was a feeder of flocks: Cain was a tiller of the ground”, and that the quarrel indicates that there was always rivalry between the tiller of the soil and the shepherd which in subsequent generations became a well-known feature of folklore.
Though Cassuto could find no specific literary evidence for this suggestion, later discoveries of Ugaritic texts lend support to his explanation.
Rashi says there are many Midrashim on the subject but does not elaborate in much detail.
Seeking midrashic material, we find reports that the brothers were always at odds and their father thought it would separate them and quieten things down if each one followed a different occupation, but in the end the hostility could not be prevented.
Another Midrash suggests that they argued over a girl; each son had a twin sister, and Cain desired the sister of Abel and sought any pretext to remove Abel from the scene.