“but he did not have regard for Cain and his offering. Cain was furious, and he looked despondent. Then the Lord said to Cain, “Why are you furious? And why do you look despondent? If you do what is right, won’t you be accepted? But if you do not do what is right, sin is crouching at the door. Its desire is for you, but you must rule over it.”” Genesis 4:5-7 CSB https://bible.com/bible/1713/gen.4.7.CSB
Cain was unhappy because God did not accept his offering. Cain wanted God to be pleased with him the way Cain wanted to please God. Cain was unwilling to please God the way God wanted to be pleased. This tension continues. We want to be god, but only the One True God is God, and only His ways matter in His judgment of the deeds of men. We are not gods, so we cannot dictate to God what is acceptable to Him, though we become angry when He doesn’t follow our script. This anger leads to sin, for which God makes us responsible and holds us accountable. God does not warn others of the danger our actions intend to inflict. Instead, each person is accountable for their actions, whether good or bad. Abel was responsible for joining Cain in the field, though Abel was innocent of wrongdoing. God did not forewarn Abel of Cain’s intent, so Cain must be accountable for his actions. Stopping Abel from harm would have allowed Cain to be no longer responsible for his actions. God does not work this way. Evil in the world is the result of people making evil choices. These evil choices have evil consequences for the innocent. All people must be reconciled to God through Jesus. Those who are reconciled to Jesus will receive eternal life. The rest of humanity is guilty and will be punished for all eternity for the evil they have done, particularly their evil of rejecting God and His way that He requires for people to be reconciled to Him through Jesus, the only Savior of the world.