ain and Abel were the first two sons of Adam and Eve. Cain was a farmer, while Abel was a shepherd. Both brothers made sacrifices to God, but God accepted only Abel's offering. This made Cain jealous of his brother and angry that God would accept someone else's sacrifice before his own. So he killed Abel—and this is why we're not supposed to be jealous.
Two different sacrifices
In Genesis 4, we see that Cain and Abel both brought sacrifices to God. Abel brought the best of his flock, while Cain brought fruit from the ground. However, God rejected Cain's sacrifice, but accepted Abel's sacrifice.
Cain was jealous that God accepted his brother's offering and not his own; so he killed him out of anger and jealousy.
Abel brought the best of his flock.
While we can’t know for sure what God told Cain, the text does provide an indication of His response to Abel and his brother. After both brothers offered sacrifices to God, “the LORD respected [Abel] but did not respect Cain and his offering” (Genesis 4:4). In other words, God accepted Abel’s sacrifice but rejected Cain’s.
The New Testament offers a similar account of why people give gifts: “all who have been baptized into Christ have put on Christ … they were buried with him through baptism into death in order that, just as Christ was raised from the dead through the glory of the Father…so we too might live a new life" (Romans 6:3-5).
The lesson here is clear: when you bring your best gift to God—yourself—He will accept you as His beloved son or daughter; but when you bring less than your best gift—yourself—He rejects it.
Cain brought fruit from the ground
Cain brought the fruit of the ground. God rejected Cain's sacrifice because it was not the right kind of sacrifice, but Abel's sacrifice was a sweet aroma to God.
Abel offered the right kind of sacrifice
Abel's sacrifice was a sweet aroma to God, while Cain's was not.
God rejected Cain's sacrifice because it wasn't good enough. In other words, it didn't meet the standards that God expected from his offerings and sacrifices. So why did Abel's work? It appeared that he used the right kind of sacrifice: “You shall not delay to offer from your harvest and your gathering [of crops], which you have prepared for yourself on the third day at its appointed time” (Exodus 23:16). Since this verse says "third day," most people assume that means Saturday evening (or Friday evening for Jews), but it could also mean Tuesday morning or Thursday afternoon depending on what interpretation you take.
We don't know exactly how long after creation week it was when Cain murdered Abel; however, we do know that God had already given His instructions about how He wanted sacrifices done by then—so there should have been no excuse for them not having been done yet! A careful reading of Genesis 4 shows us that there were probably many opportunities where they could have performed their own versions of worship services during those early years before sin came into play (think back over what happened during those first few days).
This passage tells us why Abel's offering pleased God: because he followed His instructions perfectly! We can only speculate whether or not Cain even knew what "the third day" meant at all... but even if he did understand its significance without being told explicitly by someone else (like his father), knowing something isn't the same as doing something correctly according to His wishes each time one happens upon similar circumstances later down life's road."
God rejected Cain's sacrifice
God rejected Cain's sacrifice because it was not the right kind of sacrifice. Unlike Abel's offering, Cain's was not acceptable to God. We know this because Scripture tells us that God accepted Abel's offering but not Cain's (Genesis 4:3). This tells us that there is a difference between what pleases God and what does not please Him. The Bible also teaches us that our faith should be different from the world (1 John 2:15-17). This means we should live differently than unbelievers in order for our prayers to be answered by God.
Abel's sacrifice was a sweet aroma to God, while Cain's was not.
While you can't know for sure what God said to Cain, we can infer from verse 7 that he was angry with him. As a result of Cain's sin, the ground was cursed (Genesis 4:12). But even more importantly, it seems that his sacrifice did not please God because it was not the right kind of sacrifice. It's possible that Abel's sacrifice was one of thanksgiving or praise to God for His blessings. The Bible doesn't say specifically what Abel's sacrifice was like; however, it does tell us that he brought an animal and offered it as a bloodless offering to God (Genesis 4:4).
In his book The Gospel in Genesis , C. John Collins suggests there may be another reason why Cain killed Abel—jealousy over their different types of offerings: "Cain might have felt threatened by his brother’s very existence."
Cain was jealous that God accepted Abel's sacrifice, but not his own.
In Genesis 4:1-8, we read that both Cain and Abel presented offerings to God. God accepted Abel's offering but rejected Cain's. Cain became angry and jealous of his brother because the latter had a closer relationship with the Lord: “But for Cain and his offering He had no regard” (Genesis 4:5). In this passage, it says that “God made garments of skin for Adam and his wife” (Genesis 3:21), which suggests that they were naked after they were expelled from Eden. It is possible that the skin clothes worn by humans in the Garden of Eden were made from animal skins offered by Adam or Eve after their expulsion from heaven - therefore both Adam/Eve before their fall as well as their offspring afterwards would have been able to offer sacrifices according to biblical law (Leviticus 17).
Sin is crouching
God told Cain, "Sin is crouching at the door. Its desire is for you, but you must master it." (Genesis 4:7)
This means that sin was waiting outside his house, hoping to get a chance to hurt him. It seemed like Cain should have known better than to let himself be tricked into killing Abel by an animal-like urge—but he didn't know how strong sin could be!
This means that sin was waiting outside his house, hoping to get a chance to hurt him. It seemed like Cain should have known better than to let himself be tricked into killing Abel by an animal-like urge—but he didn't know how strong sin could be! We all do stupid things sometimes because we're weak in our minds and bodies. That's why God didn't punish Cain because of any crime against Him; instead He punished him because he killed Abel out of greed and envy instead of love for his brother.
Why did can kill his brother?
Cain was jealous of his brother Abel because he thought God liked him more. Cain tried to kill Abel, but God protected him and told Cain that whoever kills a man must be punished for it. The next day, Cain again killed his brother, but this time he didn't get away with it—God punished him by sending him to live far away from other people so that no one could hurt or kill him again.
When confronted by God about Abel, Cain did not deny the deed. He simply asked where his brother was. This reveals that Cain knew what he had done and was not surprised to be questioned about it by God. We can also infer from this passage that Cain believed in God but not necessarily in His word or His commandment against killing (it is interesting to note here that people who deny the authority of Scripture often claim that such a commandment never existed).
Jealousy is rooted in sin
Here's what the Bible says: "Be not envious one of another, brethren, for envy is a sin." (James 4:1) And it goes on to say that we should be slow to anger.
Jealousy can lead to envy and anger, which are sins. So maybe we should think about whether or not jealousy is actually bad for us—and if it may be causing more harm than good.
This story is a very important one, because it shows us how sin can destroy our lives. Cain killed his brother Abel because he was jealous of him, and this sin led to an even greater tragedy for him. We should never let jealousy get the best of us!