Gary A. Herion, in his essay "Why God Rejected Cain's Offering: The Obvious Answer" ( Fortunate The Eyes That See, edited by AB Beck, AH Bartelt, PR Raabe, and CA Franke) recounts the story of when he was leading a bible study and one of the students asked why God rejected Cain's offering in Gen. 4:3-6. He began to discuss how nobody knows why God rejected it, but one of the students said "I thought it was because Cain offered produce from the ground, which in the preceding chapter had been cursed by God." Mr. Herion wrote "And there is the answer. It is as obvious as that - and as simple as that."
I have heard a number of lessons on the problem with Cain's offering. Most of them were variations of “there was no blood in the offering”, or “God knew Cain's heart was evil.” I never was satisfied with them, but I didn't have a better answer. It had never occurred to me to connect it to the what happened in the chapter before.
God commanded many animal sacrifices of which blood was an essential component; look at the first 16 chapters of Leviticus for examples. Heb. 9:22 observes “In fact, the law requires that nearly everything be cleansed with blood, and without the shedding of blood there is no forgiveness.” But the idea that God rejected Cain’s offering because it had no blood in it runs into the problem that God commanded grain offerings. For example: Lev. 2:1 “When someone brings a grain offering to the LORD it is to be of fine flour…” or Lev. 6:14 “These are the regulations for the grain offering….” Also, the Israelites were commanded to offer the firstfruits of the harvest, Lev. 23:10 “When you enter the land I am going to give you and you reap its harvest, bring to the priest a sheaf of the first grain you harvest.” This was the type of offering that Cain made, the firstfruits of the harvest, so a lack of blood was not the problem.
As for the idea that God did not accept Cain’s offering because God knew Cain heart was evil (1 John 3:12), that may have been the reason, but the bible does not say that it was. It does say in Heb. 11:4 that “By faith Abel offered God a better sacrifice than Cain did.” So, what did Abel believe that Cain did not believe?
When God created the world it was good (Gen 1:21-25, 31), but after Adam and Eve sinned God cursed the Serpent (Gen 3:14-15), he cursed Eve (Gen 3:16), but he didn't curse Adam. Instead God cursed the ground because of Adam: "Cursed is the ground because of you..." (Gen 3:17-19). Then, as the young man noted, in the next chapter Cain gave God an offering from the cursed soil. Abel believed that the land was cursed and offered God the firstfruits of his flock, an offering that was accepted. But Cain did not believe the ground was cursed and offered God the firstfruits of the cursed soil. Rather than accepting that he was wrong to make such an offering he became angry at God’s rejection of it.
Although I will admit that farming is hard work I wouldn't call the ground cursed today. What changed? In Gen 5:28-29 is an interesting statement: "When Lamech had lived 182 years he had a son. He named him Noah and said, 'He will comfort us in the labor and painful toil of our hands caused by the ground the LORD has cursed.'" Lamech said that in his time the ground was still cursed, but something would happen in Noah’s time to change that. In Gen 6:11-13 we read how the earth was corrupt, and God said "I am surely going to destroy both them and the earth." The flood was not going to destroy only the population of the earth, but it would also destroy the cursed ground. After the flood God said "Never again will I curse the ground..." (Gen 8.21). Finally, in Gen 9:20, we read of "Noah, a man of the soil...." After the flood we no longer read about the ground being cursed we read about places like the promised land “...a land flowing with milk and honey” (Ex. 3:17) and commands to offer to God the fruits of the harvest “...and now I bring the firstfruit of the soil that you, O LORD, have given me” (Deu. 26:10).
Nothing has changed in regard to what God accepts as an offering, our God is a holy God and our sacrifices are to be holy. “Therefore, I urge you, brothers, in view of God’s mercy, to offer your bodies as living sacrifices, holy and pleasing to God - this is your spiritual act of worship. Do not conform any longer to the pattern of this world, but be transformed by the renewing of your mind. Then you will be able to test and approve what God’s will is - his good, pleasing and perfect will” (Rom. 12:1-2). Cain chose to ignore what God said and did not please God by offering the fruits of the cursed ground, we can not offer acceptable sacrifices if our lives are not holy and pleasing to God.