Cain and Abel: Envy, Wrath, and God's Warning
Cain's anger grew because God respected Abel's offering and not his, yet God warned Cain about sin at the door before any murder happened. The blood of Abel cried out, and God's response to the killer joined judgment with restraint.
Why Did God Reject Cain and His Offering?
Genesis 4:1–7 never gives a stated reason for rejecting Cain's offering. What it does show is that the rejection fell on Cain as well as on what he brought, and that God met his anger with a warning and an invitation rather than abandonment.