It is human nature to want to control or manipulate God (or the gods) so we can get the outcome we want. Think about the lucky rabbit’s foot or the baseball slugger’s warmup superstitions or avoiding broken mirrors: these are little practices that are supposed to make things go well for us. Offering sacrifice is the purest form of this behavior. “I will make an offering so that God or the gods will either be pleased with me or at least will feel placated and will leave me alone.”
Now, consider Cain: we know he is a farmer, and so he is dependent on the weather, which is outside of his control. God does not ask for or desire sacrifice in order to be favorably disposed towards Cain, but Cain wants to manipulate God by offering a sacrifice. When he offers some of his produce to God, he is showing a desire to be in control.
When God is not favorably disposed to the offering, Cain shows murderous rage and jealousy towards his brother Abel. Cain wants his offering to gain favor with God, and when it doesn’t, his anger is the anger of a prideful man who feels he has been humiliated; it is the anger of an entitled man who doesn’t get what he wants.
The irony of the Cain and Abel story is that, after the murder, God shows his character by being merciful to Cain.
I think Abel’s gift of the firstborn from his flock is meant to be seen as a gift of thanksgiving toward God—it cost him more, and I think it is reasonable to assume he gave it freely and joyfully, as opposed to trying to manipulate God.
How are you giving to God today—like Cain, or like Abel?