Then the Lord said to Cain, "Where is your brother Abel?" "I don't know," he replied. "Am I my brother's keeper?" The Lord said, "What have you done? Listen! Your brother's blood cries out to me from the ground. (Genesis 4:9, 10)
The first murder on earth had taken place and the Lord was watching it all. Cain had killed his brother Abel because he was jealous and angry that God had looked with favor only on his brother's offering and not on his. Though warned by God, Cain in his anger took his brother's life. Sin had mastered him and he buried his dead brother in the ground.
When God questioned him regarding the whereabouts of his brother, he replied, "Am I my brother's keeper?"
God rebuked him and punished him. A curse was upon him that his tilling of the ground would be unfruitful and that he would be a vagabond.
How true then, what the Psalmist sings.....
The Lord is in his holy temple; the Lord is on his heavenly throne. He observes the sons of men; his eyes examine them. The Lord examines the righteous, but the wicked and those who love violence his soul hates. On the wicked he will rain fiery coals and burning sulfur; a scorching wind will be their lot. For the Lord is righteous, he loves justice; upright men will see his face. (Psalm 11:4-7)
The Apostle John exhorts us in this manner.....
Do not be like Cain, who belonged to the evil one and murdered his brother. And why did he murder him? Because his own actions were evil and his brother's were righteous. (1 John 3:12)
John goes 1 step ahead and writes.....
Anyone who hates his brother is a murderer, and you know that no murderer has eternal life in him. (1 John 3:15)
Great advice to all of us, who are believers in Jesus Christ.