#16 "Cain and Abel" Genesis 4

Now Adam knew his wife, and she conceived and bore Cain, and said, "I have acquired a man from the Lord." Then she bore again, this time his brother Abel. Now Abel was a keeper of sheep, but Cain was a tiller of the ground. And in the process of time it came to pass that Cain brought an offering of the fruit of the ground to the Lord. Abel also brought of the firstborn of his flock and of their fat. And the Lord respected Abel and his offering, but He did not respect Cain and his offering. And Cain was very angry and his countenance fell. 

So the Lord God said to Cain, "Why are you angry? And why has your countenance fallen? If you do well, will you not be accepted? And if you do not do well, sin lies at the door. And its desire is for you, but you should rule over it."

Now Cain talked with Abel his brother; and it came to pass, when they were in the field, that Cain rose up against Abel and killed him.

Then the Lord said to Cain, "Where is Abel your brother?"

He said, "I do not know. Am I my brother's keeper?"

And He said, "What have you done? The voice of your brother's blood cries out to Me from the ground. So now you are cursed from the earth, which has opened its mouth to receive your brother's blood from your hand. When you till the ground, it shall no longer yield its strength to you. A fugitive and a vagabond you shall be on the earth."

And Cain said to the Lord, "my punishment is greater than I can bear! Surely You have driven me out this day from the face of the ground; I shall be hidden from Your face; I shall be a fugitive and a vagabond on the earth, and it will happen that anyone who finds me will kill me."

And the Lord said to him, "Therefore, whoever kills Cain, vengeance shall be taken on him sevenfold." And the Lord set a mark on Cain, lest anyone finding him should kill him. Genesis 4:1-15

Knew his wife: They had intercourse and she conceived, then bore Cain. There does not seem to be a break here and it does not say that Adam knew his wife again, or that she conceived again. It simply states that she bore again, which could be an indication that the boys were twins. 

Firstborn of his flock: The best of not only what he had, but a blood offering and consistent with his faith and obedience to God.

By faith Abel offered to God a more excellent sacrifice than Cain, through which he obtained witness that he was righteous, God testifying of his gifts; and through it he being dead still speaks. Hebrews 11:4 NKJV

To Jesus the Mediator of the new covenant, and to the blood of sprinkling that speaks better things than that of Abel. Hebrews 12:24

Abel's offering showed that he believed and he was the first to be murdered for his faith. The Lord testifies of this act of physical obedience and its origin in belief. It is a temporary covering and symbolic of that which will follow in the redemptive sacrifice of God Himself. Jesus blood will finish the old covenant and atone for all those who believe, and for all of eternity.

For it pleased the Father that in Him all the fullness should dwell, and by Him to reconcile all things to Himself, by Him, whether things on earth or things in heaven, having made peace through the blood of His cross. Colossians 1: 19&20