Why God Did Not Favor Cain's Offering
Genesis 4 does not explain why God favored Abel's offering and not Cain's. It shows what God did next: he questioned Cain, warned him about sin, and called him to do well rather than resent his brother.
Why Did God Reject Cain? Genesis 4:3–7 Explained
Genesis never tells us the reason Cain's offering was not respected. What it does show is God speaking to Cain before any violence, questioning his anger and calling him to do well.