Fred "Felice" Rizzo, Ph.D., contends that Cain killed Abel because Abel was a cattle-ranching animal-killer. When Abel violated the THOU SHALT NOT KILL commandment, Cain responded with the first justifiable homicide. Cain knew that using force to stop abuse or murder was a permissible act of vicarious self-defense.
Rizzo further explains the etymology of Abel's name. It translates to anti-God. "Ab" is the prefix that negates, while "El" is an archaic word for God. The ancient storytellers passed down the Cain and Abel narrative and forever let it be known which brother was evil by labeling Abel as anti-God. According to Rizzo's etymological research, all words derived from Abel pertain to something evil, while words from Cain are happy or peaceful. For instance, the Jewish holiday Chanukah is derived from Cain's name.
Source: https://www.adaptt.org/animal-rights/the-bible-jesus-and-veganism.html?fbclid=IwAR0fLJibE66T_xPtYJ4_om5lfJgKNYIIgGp5-tQzJr5wAulyBDfUkP290_M