What does Genesis 4:9 mean?
Following Cain's murder of his brother Abel in a field, God comes to confront Cain. As He did with Adam and Eve following their sin in the garden, God begins with a question He already knows the answer to: Where is your brother? God provides Cain the opportunity for confession. When God gave this option to Adam, he reluctantly confessed to what he had done. This was not ideal, but it at least reflected a willingness to obey God (Genesis 3:8–13).Instead of taking this approach, Cain lies to God and remains defiant. He brazenly claims not to know where Abel is. He then asks a question siblings have been quoting to their mothers for generations: "Am I my brother's keeper?" This not only represents dishonesty, but disrespect. Cain flippantly rejected any responsibility for his murdered brother in a way which implies it's wrong of God to even ask the question.
In modern language, Cain is essentially telling God, "Why is Abel my problem?"