"If you do well, will you not be accepted? And if you do not do well, sin is crouching at the door. Its desire is for you, but you must rule over it.”
Cain spoke to Abel his brother. And when they were in the field, Cain rose up against his brother Abel and killed him. Then the Lord said to Cain, “Where is Abel your brother?” He said, “I do not know; am I my brother's keeper?”
After Cain had offered an unpleasing sacrifice to the Lord, the Lord had warned Cain to bridle his anger. Like a lion stalks its prey, sin was waiting for the proper moment to ambush and pounce on Cain. The Lord had warned him to be vigilant and ready to reign over his emotions.
Instead, Cain foolishly did not heed the Lord’s advice. He acted on his emotions and plotted a plan to get back at Abel (and the Lord). Cain lured his brother into the field where he knew that they would be alone. Then, he killed Abel. This pre-meditated murder was the first homicide in the history of mankind.
The Lord, being an omniscient and omnipresent God, knew exactly what Cain had done. He not only knew that Cain would commit this horrible crime against humanity, but in His sovereignty, He seemed to plan for this evil to occur. Therefore, His question to Cain was strictly rhetorical, and Cain responds in a spirit of sarcasm, “Am I my brother’s keeper?”
The rest of the story is that the Lord cursed Cain and his descendants for these hideous sins. The Lord banished Cain from the land of his parents, making him wander the earth. He also made farming, something that came easy to Cain, difficult for him and his generations. From then on, Cain’s formerly successful farming methods would have no effect.
When we are confronted with our sin, let us not act in a spirit of sarcastic cynicism as Cain had done. Instead, let us come to the Lord with a heart full of repentance. If we confess our sins, the Lord has promised to forgive us (I John 1:9). Furthermore, let us prevent even more sin by taking the Lord’s advice and practicing self-control over our emotions.