The sin of Adam and Eve would have tragic consequences that would become evident in their very own family. Indeed, the larger human family has repeatedly duplicated the dysfunctional dynamics that sin produced in the first human family. A thoughtful consideration of the story of Cain and Abel yields some interesting lessons.
Adam and Eve had two sons—Cain, the firstborn, and Abel. (They would also have other sons and daughters, too, as mentioned in Genesis 5:4 Genesis 5:4And the days of Adam after he had begotten Seth were eight hundred years: and he begat sons and daughters:
American King James Version×. Yet they apparently had no other sons until the death of Abel, as Seth seems to be the next male child in line, compare Genesis 4:25 Genesis 4:25And Adam knew his wife again; and she bore a son, and called his name Seth: For God, said she, has appointed me another seed instead of Abel, whom Cain slew.
American King James Version×). Cain, we are told, became a tiller of the ground, a farmer. Abel became a shepherd. As to the acceptance of Abel’s offering and the rejection of Cain’s, some have suggested that there was something wrong in Cain bringing a grain offering. Yet we later see grain offerings as perfectly acceptable to God. Indeed, God said the grain offering was to be burnt “on the altar for a sweet aroma, as a memorial to the Lord…. It is most holy, like the sin offering and the trespass offering” (Leviticus 6:15 Leviticus 6:15And he shall take of it his handful, of the flour of the meat offering, and of the oil thereof, and all the frankincense which is on the meat offering, and shall burn it on the altar for a sweet smell, even the memorial of it, to the LORD.
American King James Version×, Leviticus 6:17 Leviticus 6:17It shall not be baked with leaven. I have given it to them for their portion of my offerings made by fire; it is most holy, as is the sin offering, and as the trespass offering.
American King James Version×). So what was the problem? Genesis 4:4 Genesis 4:4And Abel, he also brought of the firstborn of his flock and of the fat thereof. And the LORD had respect to Abel and to his offering:
American King James Version×tells us that Abel brought from the “firstlings” of his flock, but no such indication of giving God the first or best is attached to Cain’s offering in the previous verse. Perhaps this was due to Cain’s overall attitude. Genesis 4:5 Genesis 4:5But to Cain and to his offering he had not respect. And Cain was very wroth, and his countenance fell.
American King James Version×states, “But [God] did not respect Cain and his offering.” Notice that it was not just the offering that God did not respect, but Cain himself! Indeed, that may be the very reason that God did not accept his offering. We are often told in Scripture that God loathes the sacrifices, festivals and even prayers of those who are guilty of great wrong and yet are unrepentant (see Isaiah 1:10-15 Isaiah 1:10-15  Hear the word of the LORD, you rulers of Sodom; give ear to the law of our God, you people of Gomorrah.  To what purpose is the multitude of your sacrifices to me? said the LORD: I am full of the burnt offerings of rams, and the fat of fed beasts; and I delight not in the blood of bullocks, or of lambs, or of he goats.  When you come to appear before me, who has required this at your hand, to tread my courts?  Bring no more vain oblations; incense is an abomination to me; the new moons and sabbaths, the calling of assemblies, I cannot away with; it is iniquity, even the solemn meeting.  Your new moons and your appointed feasts my soul hates: they are a trouble to me; I am weary to bear them.  And when you spread forth your hands, I will hide my eyes from you: yes, when you make many prayers, I will not hear: your hands are full of blood.
American King James Version×). When such a person “offers a grain offering, [it is] as if he offers swine’s blood” (Isaiah 66:3 Isaiah 66:3He that kills an ox is as if he slew a man; he that sacrifices a lamb, as if he cut off a dog's neck; he that offers an oblation, as if he offered swine's blood; he that burns incense, as if he blessed an idol. Yes, they have chosen their own ways, and their soul delights in their abominations.
American King James Version×). God recognized that Cain was on the verge of allowing sin to control him (Genesis 4:7 Genesis 4:7If you do well, shall you not be accepted? and if you do not well, sin lies at the door. And to you shall be his desire, and you shall rule over him.
American King James Version×)—to manifest itself in real action.
We are told that Abel, on the other hand, offered a better sacrifice because it was offered by faith, through which he was considered righteous (Hebrews 11:4 Hebrews 11:4By faith Abel offered to God a more excellent sacrifice than Cain, by which he obtained witness that he was righteous, God testifying of his gifts: and by it he being dead yet speaks.
American King James Version×; Matthew 23:35 Matthew 23:35That on you may come all the righteous blood shed on the earth, from the blood of righteous Abel to the blood of Zacharias son of Barachias, whom you slew between the temple and the altar.
American King James Version×). Faith comes by hearing God’s instruction (Romans 10:17 Romans 10:17So then faith comes by hearing, and hearing by the word of God.
American King James Version×). God’s commandments must have been transmitted through Adam and Eve. And God must have even prescribed rules for worship at some point, or else how would Cain and Abel have known to bring sacrifices? Abel was obedient—through faith.
Cain’s rejection roused him to anger and jealousy—though he may have already had these emotions to some degree. In any event, he did not master his urges, as God told him to (Genesis 4:7 Genesis 4:7If you do well, shall you not be accepted? and if you do not well, sin lies at the door. And to you shall be his desire, and you shall rule over him.
American King James Version×). Instead, he murdered his brother. Later, God confronted Cain: “The voice of your brother’s blood cries out to Me from the ground” (Genesis 4:10 Genesis 4:10And he said, What have you done? the voice of your brother's blood cries to me from the ground.
American King James Version×). When someone is said to cry out to God, the cries are usually for relief, protection or vengeance. Abel’s blood, figuratively speaking, cried out for vengeance. This is confirmed by Cain’s fear that vengeance would be taken out upon him by anyone who found him, and by God’s remarks in Genesis 4:15 Genesis 4:15And the LORD said to him, Therefore whoever slays Cain, vengeance shall be taken on him sevenfold. And the LORD set a mark on Cain, lest any finding him should kill him.
American King James Version×, which explicitly connect vengeance with the context. This is interesting because the book of Hebrews states that the blood of Jesus “speaks better things than that of Abel” (Hebrews 12:24 Hebrews 12:24And to Jesus the mediator of the new covenant, and to the blood of sprinkling, that speaks better things that that of Abel.
American King James Version×). Why? Because Abel’s blood sought vengeance, which was well and just, but Christ’s blood offers mercy and forgiveness to those who will accept it, which is better.
Cain departed and headed east to the land of Nod, meaning “vagabond” or “wandering”—thus perhaps not indicating an actual geographic name. And then we see mention of Cain’s wife, who must have been one of his sisters. “The problems associated with incest, addressed in Leviticus 18, would not have occurred when the genetic pool was pure and unpolluted” (Nelson Study Bible, note on Genesis 5:4 Genesis 5:4And the days of Adam after he had begotten Seth were eight hundred years: and he begat sons and daughters:
American King James Version×). Today, as defined by God in Leviticus 18, incest is a sin.