In our study of Genesis chapter four, we look at how the curse of sin was passed on to the next generation. We will also see how that generation began a downward spiral that would eventually end in God's judgment by flood.
"Adam lay with his wife Eve, and she became pregnant and gave birth to Cain. She said, 'With the help of the Lord I have brought forth a man.' Later she gave birth to his brother Abel. Now Abel kept flocks, and Cain worked the soil." NIV translation
So, Adam and Eve started the family with two boys. One (Cain) was a farmer while the other (Abel) was a shepherd. We should understand that Adam and Eve would have thought that Cain was the man spoken of in the curse to the serpent (see chapter 3) that would crush his head.
"In the course of time Cain brought some of the fruits of the soil as an offering to the Lord. But Abel brought fat portions from some of the firstborn of his flock." NIV translation
"In the course of time" speaks to the fact that these offerings were brought to the Lord on the Sabbath. We see that Abel brought fat portions from the firstborn of his sheep while Cain brought some of the grain from his crops.
"The Lord looked with favor on Abel and his offering, but on Cain and his offering he did not look with favor. So Cain was very angry, and his face was downcast." NIV translation
The Lord accepted the offering of Abel but not that of Cain. We may ask ourselves why this is so and the answer is very simple. Man was created to be a caretaker of all that God has created (see Genesis 2). Sin resulted in man working the ground to grow his food instead of just picking fruit from the trees that God provided. The fat portions that Abel brought were a praise to God for what he had provided while the grain that Cain brought was a result of his work (work that God had not created man for). This was, in fact, an offering of works to God instead of an offering of faith. We see in this also the struggle between the law and grace that is evident in the world today. Abel's offering was thanking God for His provision (grace) while Cain's offering was a picture of the coming law. Only the grace of God demonstrated through our Lord Jesus Christ has the power to make us right with God.