Cain and Abel go to God with their sacrifices. Cain is a farmer, and brings food "from the ground." Abel is a shepherd, and brings God the "firstborn from his flock." God accepts Abel's offering, but not Cain's. We don't really know for sure why this is the case. It probably had something to do with the offering itself, though in the end, it was the heart of Cain which was against God. Remember that God commanded sacrifices from the ground years later, and many times we see this as acceptable. The difference had to have been Cain's heart.
The proof is in Cain's reaction. At this point he could have done two things. First, he could have asked God why his sacrifice wasn't accepted. The other thing he could have done is search his own heart to see if there was something within himself that needed work. Instead, "Cain was very angry."
God, in His mercy, comes to Cain. "If you do well, won't your sacrifice be accepted?" This question from God is an important one. It isn't that God has rejected Cain outright. In fact, there is the opportunity in this for Cain to receive God's mercy. God will accept what Cain offers if Cain will offer it in a proper way.
God then warns Cain. Now, we all know what Cain is going to do, but Cain at this point had not killed his brother. So God warns him. "Sin is crouching at your door." This is a stern warning from God to watch the temptation to act in his anger.
Cain kills his brother anyway.
Read that carefully. Warned by God, Cain ignores the warning and takes his anger out on his brother. He was in the wrong, but instead of bearing the weight of his guilt, he took it out on his brother. Abel, though he had done nothing wrong, was murdered. Cain, though warned by God, kills his brother.
Then comes the really merciful part of the story. This is a part of the story that we sometimes forget, and when I was younger, I didn't really understand it. God sends Cain away from where he was to be a wanderer. That I get. Cain, though, is worried. Look at what he says to God.
"My punishment is greater than I can bear.
Behold, you have driven me today away from the ground,
and from your face I shall be hidden.
I shall be a fugitive and a wanderer on the earth,
and whoever finds me will kill me."
I remember reading this when I was younger and wondering what his complaint was. Sure, he might get killed, but isn't that what he deserves? I mean, he kills his brother, and then thinks God should protect him? What's amazingly merciful, is that this is exactly what God does. God protects Cain, even though Cain had rejected Him.
Then the LORD said to him, “Not so!
If anyone kills Cain, vengeance shall be taken on him sevenfold.”
And the LORD put a mark on Cain, lest any who found him should attack him.
This is the mercy of God at work, and I have found it to be true in my life as well. I try to remind myself and my congregation that God, in His grace and mercy, saved me from all the sin in my past. It is even greater when you think that God, in His grace and mercy, saved me though He knew I would fail Him many more times after He saved me.
Praise be to the God and Father of our Lord Jesus Christ!
In his great mercy he has given us new birth into a living hope
through the resurrection of Jesus Christ from the dead,
and into an inheritance that can never perish, spoil or fade— kept in heaven for you,
who through faith are shielded by God’s power
until the coming of the salvation that is ready to be revealed in the last time.
- I Peter 1:3-5.