Cain's first sin was a lack of faith—he did not believe what God had said and therefore did not do what God instructed.
According to Les Feldick, Cain was 'destitute of faith.' God had instructed that sin required a blood sacrifice, but Cain rationalized and brought the fruit of his own labor instead. This unbelief set off a chain reaction of envy, anger, and ultimately murder.
Genesis 4:3-5 — This passage records Cain's offering being rejected, showing that he did not follow God's instruction while Abel did.
In Genesis 4:3-5, we read that Cain brought of the fruit of the ground as an offering to the Lord, while Abel brought the firstlings of his flock. God had respect unto Abel and his offering, but unto Cain and his offering He had not respect. The Bible does not explicitly state in Genesis why Cain's offering was rejected, but Hebrews 11:4 says that Abel offered a more excellent sacrifice by faith. The Bible shows Cain's reaction: he became very angry, and his countenance fell.
Les Feldick emphasizes that the root of Cain's problem was a lack of faith. He did not believe what God had said. God had instructed that when conscience convicted of sin, a blood sacrifice was required. Abel believed and brought a blood sacrifice, but Cain rationalized and brought the fruit of his own labor. This unbelief was Cain's first sin, and from it flowed envy, anger, and ultimately murder.
Les explains that envy and jealousy can eat at a person's inner being and eventually come to the surface. Cain became envious of Abel's relationship with God and of Abel being accepted. This jealousy led him to murder his brother. The chain begins with unbelief, which leads to coveting or envy, and then to outward sin.
God did not immediately punish Cain. Instead, He pleaded with him, asking, 'Why art thou wroth? and why is thy countenance fallen?' (Genesis 4:6). Les points out that God was saying, if you would just do what I told you, I would accept you. The offer of reconciliation was open, but Cain refused.
Abel brought a blood sacrifice as God had instructed, because he had faith. Cain brought a bloodless offering, what he thought God would accept. He did not do what God said, making him without faith — and without faith it is impossible to please God.
Envy Leads to Outer Sin
Les explains how envy and jealousy, first seen in Cain, are always the trigger for breaking God's commands.
God's Plea to Cain
Les notes that when Cain's countenance fell, God asked why he was angry, revealing God's desire for Cain to be reconciled.
Cain's Rationalization
Les says Cain rationalized God's instruction and brought his own produce instead of the required blood sacrifice.
Cain vs. Abel: Why God Accepted One Offering and Rejected the Other
Come back to Genesis chapter 4, and I'm always amazed at how many people who have been in church all their life have never caught why Abel's sacrifice was accepted and Cain's was not. I mean, I just have it come up constantly. All right? Verse 5 again, Unto Cain and to his offering God had no respect. And now, just like human beings today, see, the human race hasn't changed one bit.
Cain's Lack of Faith
Les explicitly states that Cain was 'destitute of faith'—he didn't believe what God said, evidenced by his bloodless offering.
The Root: Not Doing What God Said
Les says Cain's big problem was that he didn't do what God said, making him without faith, and 'there the ball starts rolling.'
God's Grace and the Call to Faith
Les emphasizes that God pleaded with Cain, saying if he would just do what He said, he would be accepted—showing the issue was faith.
Who Did Cain Marry? & The Mystery of Enoch (Genesis 4-5 Bible Study)
I think, and I haven't made it plain before, I think perhaps after Adam and Eve left the garden of Eden, you remember it said back there in chapter 3 that God placed angels at the gate of the garden with flaming swords reaching each way. I would agree with those who maintain that this was probably the place where they met the Lord with their sacrifices.
Genesis 4:3-5: And in process of time it came to pass, that Cain brought of the fruit of the ground an offering unto the LORD. And Abel, he also brought of the firstlings of his flock and of the fat thereof. And the LORD had respect unto Abel and to his offering: But unto Cain and to his offering he had not respect. And Cain was very wroth, and his countenance fell.
This is the biblical account of Cain's and Abel's offerings, showing God's rejection of Cain's offering and Cain's angry reaction.
Genesis 4:6-7: And the LORD said unto Cain, Why art thou wroth? and why is thy countenance fallen? If thou doest well, shalt thou not be accepted? and if thou doest not well, sin lieth at the door. And unto thee shall be his desire, and thou shalt rule over him.
God's response to Cain's anger reveals that acceptance was possible if Cain did well, but sin was waiting if he did not.
Hebrews 11:4: By faith Abel offered unto 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 speaketh.
This verse contrasts Abel's faith with Cain's lack of faith, indicating why Abel's sacrifice was accepted.
Hebrews 11:6: But without faith it is impossible to please him: for he that cometh to God must believe that he is, and that he is a rewarder of them that diligently seek him.
Les cites this principle to explain that Cain's lack of faith meant he could not please God.
According to Les Feldick, Cain's first sin was his lack of faith. He did not believe what God had said about the need for a blood sacrifice, so he brought an offering of his own making. This unbelief led to envy, anger, and eventually murder.
The Bible does not record Cain repenting. Instead, when God asked where Abel was, Cain lied and said he did not know, adding deception to his list of sins. Les Feldick notes that Cain's path of unbelief led to further sin.
Watch the Teaching: Understanding Cain and Abel: Faith, Sin, and Civilization Explained