Why was Cain’s sacrifice rejected in Genesis 4 and what are we meant to learn from this event? We are not told what was missing from the offering. There are no explicit revealed pre-existing criteria. All we have is the comparison to Abel’s accepted offering. Abel’s offering was his best, Cain’s perhaps not. What the incident revealed was an underlying issue with Cain’s pride, which led to murder.
Cain and Abel are presented to us as the two offspring of Adam and Eve. Ultimately both are “lost” and the third son Seth born after these events is presented as the firstborn in their absence (Gen 5:4). Abel was a shepherd and Cain a farmer (Gen 4:2).
As an aside – there is something strange about Abel keeping flocks. According to Gen 4:20-22 it wasn’t until 6 generations after Cain that animal husbandry and metal tools (which are pretty useful for shepherds) became a thing. The compiler of Genesis didn’t worry about smoothing out such contradictions.
The two occupations potentially point to a difference in the brothers. The NET notes link these occupations back to the earlier expressions in Genesis 2-3:
Abel is occupied with sheep, whereas Cain is living under the curse, cultivating the ground
But were shepherds good and agriculturalists bad typically speaking? Being a shepherd generally is seen as a good thing in the Scripture. The patriarchs were nomadic herdsmen. Moses and David were shepherds. In the New Testament Jesus is the Good Shepherd. Some bad shepherds do get mentioned occasionally so it’s not all good. There are examples of good farmers in Scripture also eg Boaz, Naboth and Isaac in Gen 26:12. Part of the initial problem in Gen 2:5 is that there was no one to cultivate the ground – which prompted the creative acts of God. The original task of Adam was working and keeping the garden Gen 2:15. So farming was the original human occupation. The brother’s differing occupations seems a poor proxy for their character or “goodness”.
On what basis could the sacrifice be rejected?
Some might protest that without any revealed criteria any rejection was invalid. If God hadn’t revealed what He wanted He couldn’t reject anything. This protest fails somewhat when we consider that the Pentateuch – regardless of your position on when and how it was created – is a literally unit. As Waltke says:
Although the Cain and Abel story probably enjoyed preliterary independence, it must now be read as part of the Pentateuch
The story of Cain and Abel forms part of the same work that contains the Mosaic sacrificial code – whoever completed the Pentateuch wasn’t compelled to repeat details endless. That the text presupposes consistency of Divine expectation is a fairly safe assumption.
So why was Cain’s offering rejected?
A traditional explanation has been that Cain’s offering did not include involve the shedding of blood so was inappropriate (see for example Robert Roberts and Whittaker). This explanation is unsatisfactory given the evidence of the passage. Gen 4 refers to all the offers as a minhah offering. The Complete Word Study Dictionary defines the word as:
minḥāh: A feminine noun meaning a gift, a tribute, an offering. This word is used to signify a gift as in the peace gifts that Jacob presented to Esau (Gen. 32:13). Secondly, it signifies a tribute. An example of the use of this word is Judges 3:15, where Ehud was sent from Israel to Moab on the pretense of bringing a tribute. Perhaps the most frequent use of this word is to denote a grain offering. Grain offerings were brought on pans, suggesting cakes (Lev. 2:5) and mixed with oil and other substances (Num. 6:15).
The expression is the grain offering. The minhah is
most closely associated with the grain offering later in Leviticus 2. They appear to be intended to express gratitude to God for his bounty.
The record in Lev 2 makes it fairly clear that the offering had to be first rate quality. The grain/meal offering was the best grain and/or the first fruits. The best was offered.
As Waltke points out (after a review of the data):
lexical study for the term designating Cain’s offering gives no basis for thinking it was rejected because it was bloodless. In fact, of the many expressions for presentations to God which were available to Moses, he could not have used a more misleading term if this were his intended meaning
The record does distinguish the two offerings though as per the NET:
|Cain brought some of the fruit of the ground for an offering to the Lord||Abel brought some of the firstborn of his flock —even the fattest of them. And the Lord was pleased with Abel and his offering|
Abel’s offering was his best – consistent with the Leviticus 2 spirit of the meal offering. The commendation of Abel’s greater sacrifice (Heb 11:4) according to the writer of Hebrews reflected Abel’s faith and righteousness. By contrast the Genesis narrator is suggesting Cain’s offering was not his best.
Previously I understood this incident as a demonstration that we have to serve God as He wishes. Cain didn’t bring the right offering. I was wrong. The language and words used point to a bigger truth. Our attitude to God’s service matters, He wants the best.
 Biblical Studies Press. (2005). The NET Bible First Edition; Bible. English. NET Bible.; The NET Bible. Biblical Studies Press.
 Matthews, V. H., Chavalas, M. W., & Walton, J. H. (2000). The IVP Bible background commentary: Old Testament (electronic ed., Ge 4:1–7). Downers Grove, IL: InterVarsity Press.