[Answer]
Abel raised sheep for one reason. his whole work life hinged on one thing.
He raised sheep specifically for an offering. For sacrifice. So when Cain gave of ” his sweat of the land” it didn’t mean as much because he gained materially from his work. Abels sacrifice was selfless in nature. Which is why God esteemed his offering over Cain’s. God and the relationship with God was the priority to Abel he worked to continue that relationship. Abel had no benefit in and of himself. he wholly relied on God.
that’s why it pissed off satan(so he enraged Cain with envy to kill Abel) that’s why it pissed off Cain (not understanding the difference of offerings) And that’s why it pleased God.
* Extra tidbit- notice from that point the communion with God in the relationship with people became more and more separated. Cain killed the key to close that separation gap between Gods commune with man.
Amazing.
s
Telltheworldtheword 
Very Good!