How do you respond when others seem to be favoured over and above you? Are you happy for them? Does it spur you on to do better or does it cause resentment and jealousy? God has accepted Abel’s sacrifice, the younger brother preferred to the older being a theme that will develop throughout the Old Testament. How will Cain respond to this?
Read Genesis 4:6-16
God speaks to Cain, observing his angry demeaner (v6). He encourages him to do what is right, or to act righteously. This helps us to add an other piece into the jigsaw puzzle, the acceptance of Abel’s offering is linked to righteousness. He is in effect justified. The possibility of acceptance, is not withheld from Cain but freely offered to him. However, God warns the older brother that danger is still there, a test is to come. Notice the personification of sin here, laying in wait to pounce upon Cain. Sin desires Cain, in other words to possess, control and master him. However, Cain must master, rule over, subdue sin. He must learn self-control. The structure and vocabulary here echoes Genesis 3:16 where it is the wife who desire’s her husband but he will master her (v7). 
Cain speaks to his brother. What is said is left un reported. In fact, in Hebrew it’s more abrupt, translating directly along the lines of “And Cain said to Abel, his brother …. And when they were in the field.” The speech almost appears to have dropped out, communication has broken down and violence ensues. Cain murders Abel (v8).
In Eden, God asked Adam where he was. Here, he asks Cain where his brother is. Cain denies both knowledge and responsibility (v9). God will not allow Cain to get away with this dismissive response. He demands a full account. Abel’s blood itself cries out, demanding justice (v10). God passes judgement on Cain. Notice the way things have developed from Eden where the ground was cursed but not Adam himself. Now Cain himself is cursed. If cursed from the ground, this suggests exile and separation from it. He will no longer be able to live as a settled farmer off of the produce of the land. Just as God had accepted Abel’s offering and rejected Cain’s, not the ground receives Abel’s blood but rejects Cain (v11-12).
Cain protests his punishment as too heavy. This isn’t a good sign. He remains more concerned for himself, more resentful of God, still lacking in true remorse (v13). He now spells out in his own words the judgement he is under, banished both from the ground and from God’s face. However, of greatest concern to Cain is not his relationship to God but the threat of others. He fears that other men will in turn seek his life, seek vengeance on him for Abel (v14). God offers grace in judgement. Cain is protected from revenge, anyone who attacks him will be held accountable (v15).
Cain now moves away, he has little choice but to begin life as a nomad due to the curse but notice too that Cain goes away from God’s presence. Now, remember that God is present everywhere, so Cain cannot truly leave his presence. However, God has made his manifest presence in a specific place. Also, I believe that Cain’s move represents his heart decision to seek a life away from God (v16).
Strikingly, Adam appears to be absent from the narrative. There’s focus on Eve naming her sons but Adam doesn’t get involved. It could be that because of the escalation of sin that God stepped in to judge again, to teach Adam and Eve. It could also be possible that God spoke through the judgement of Adam. If so, then Cain would be going from his father’s literal presence and a symbol of leaving God’s presence. It is also possible though that Adam, having failed to take responsibility with regard to the Tree, once more fails to step up to the plate.
What about you and me? I started by asking the question about how we respond when others are preferred or our efforts seem to be rejected. Cain’s response was an ungodly one. Let’s be careful not to follow his pattern. This means that we also need to be those who positively accept God’s verdict, welcoming the blessing that is poured out on others and allowing God’s Word to convict us.
 As I observed on Genesis 3:16, the ESV’s insertion of “contrary to” after desire is unsubstantiated and unhelpful in both examples.