After the fall, two brothers brought offerings to the Lord, but only one was accepted:

And in the process of time it came to pass that Cain brought an offering of the fruit of the ground to the Lord. Abel also brought of the firstborn of his flock and of their fat. And the Lord respected Abel and his offering, but He did not respect Cain and his offering. And Cain was very angry, and his countenance fell. So the Lord said to Cain, “Why are you angry? And why has your countenance fallen? If you do well, will you not be accepted? And if you do not do well, sin lies at the door. And its desire is for you, but you should rule over it.” (Gen 4:3-7).

Why did God reject Cain’s offering?

A popular answer is that God rejected it because it was not a blood offering. I think that’s wrong for two reasons: First, the text does not say that. Second, God later commanded grain offerings (Leviticus 2; Lev 6:14-23), so we know there’s nothing wrong with it in principle.

So why was Cain’s offering rejected?

God explained why: “If you do well, will you not be accepted?”

Cain’s offering was not accepted, because Cain was not doing well. Instead, he was doing evil. As John tells us, Cain’s life was characterized by evil even before he murdered Abel:

For this is the message that you heard from the beginning, that we should love one another, not as Cain who was of the wicked one and murdered his brother. And why did he murder him? Because his works were evil and his brother’s righteous (1 John 3:11-12).

God will not accept an offering from someone who is doing evil. That’s why God warned Cain against sin: “sin lies at the door. And its desire is for you, but you should rule over it.” Sadly, instead of ruling over it, sin was evidently ruling over Cain. That’s why he killed Abel. And because his works were evil, God did not accept his offering.

Thousands of years later, Jesus taught about this principle—and I wonder if He had Cain and Abel in mind:

“You have heard that it was said to those of old, ‘You shall not murder, and whoever murders will be in danger of the judgment.’ But I say to you that whoever is angry with his brother without a cause shall be in danger of the judgment. And whoever says to his brother, ‘Raca!’ shall be in danger of the council. But whoever says, ‘You fool!’ shall be in danger of hell fire. Therefore if you bring your gift to the altar, and there remember that your brother has something against you, leave your gift there before the altar, and go your way. First be reconciled to your brother, and then come and offer your gift” (Matt 5:21-24).

What’s the principle?

When you worship God, is your heart right? Specifically, are you angry with someone? Are you harboring hatred for your brother, sister, father, co-worker, in-laws, or neighbors?

If so, then God will not accept your “offering”—whether it’s a prayer, a financial gift, a work, or some other sacrifice—until you start loving them again.

That should tell you what God really wants in worship—for you to love your brother. Without love, your act of worship is neither accepted, nor profitable (cf. 1 Cor 13:3).

To paraphrase what God told Cain, “If you love, will you not be accepted?”