1. Human beings are always being tempted by Evil and the Devil.
2. By eating the forbidden fruit their relationship with God is weakened and God’s trust in them has weakened also. After this they learn from their mistakes and will not do it again.
3. They can try not to do anything that would ruin their relationship with God which is basically the same as not sining and they would learn from their mistakes.
4. He can not control his anger and his Jealousy for his brother
5. He stopped the violence by punishing Cain and making him live with the guilt
6. I think his life should have been spared to save someone from killing him but his life should be punished and he should be made to live with the regret of killing his brother