Just read this part last night, God told Cain to just “do what is right” and everything would be fine. Sounds like me talking to my rebellious offspring.
Gen 4:6-7
6 Then the LORD said to Cain, “Why are you angry? Why is your face downcast? 7 If you do what is right, will you not be accepted? But if you do not do what is right, sin is crouching at your door; it desires to have you, but you must master it.”
It wouldn’t have been all that hard for Cain either. He was a fruit and vegetable farmer, and Abel specialized in livestock. They could have cooperated furnishing Abel with a larger variety of food to personally consume and furnishing Cain a sacrifice of the kind that pleased God (it was a foreshadowing of the Lamb of God which is why fruits and vegetables would not do). It was Cain’s stupid ego and pride that was his downfall.
This is a great story to understand how much God loves us and his creation. The story is called Cain and Abel but it should be called Cain and God. The story shows God repeatedly reaching out with love to Cain even up to and including his punishment.