Cain's jealousy towards Abel arises from the favor with which God looks upon Abel and his sacrifices. Even though God was important in Cain's life -- and he did give God sacrifices -- Abel gave him the first and the best of everything, something Cain didn't do. Because Cain didn't put God first, he opened up a doorway for things like jealousy and thoughts of murder to enter his life. In your class or small group, discuss the benefits of putting God first with your tithes, offerings, relationships and work.
In verse 9 of Genesis 4, after God confronts Cain about Abel's death, Cain asks, "I don't know, am I my brother's keeper?" Cain was Abel's older brother, but God doesn't answer this question with a simple "yes" or "no." Discuss what it means to be your brother's (or sister's) keeper, and whether we're responsible for acting as a keeper for our siblings. Ask the class to think of other examples from scripture to back up their arguments about whether we are responsible for our brothers. If there is a unanimous "yes" in the room, ask a few people to play the devil's advocate and come up with reasons why we shouldn't be our brother's keeper. Finally, discuss why it is important to act as your brother's keeper.
Ultimately, the story of Cain and Abel can be reduced to the imperfections of one man getting the best of him. In the story, man had already fallen from the grace of God after Adam and Eve ate from the forbidden tree. God knew that man had imperfections, but he still loved them and communicated with them. In verses 6 and 7, God says, "Why are your angry? Why is your face downcast? 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 rule over it." Discuss the deeper meaning in these verses and what it means to do right even if all humans are imperfect and can't avoid sin completely.
When God punishes Cain after the death of Abel, Cain is worried and says, "whoever finds me will kill me" because God banished him from the land and he would live as a wanderer for the rest of his life. However, verse 15 says, "'Not so; anyone who kills Cain will suffer vengeance seven times over.' The the Lord put a mark on Cain so that no one who found him would kill him." Even though God was upset with Cain and had to punish him, he still looked after him and put a mark on him letting everyone know that God protected him. Discuss this idea and how it relates to the Christian idea of God as our Father in Heaven. Discuss what this means to each person in the group, and what it reveals to you about God's character.