KJV Genesis 4 : 15
And the LORD said unto him, Therefore whosoever slayeth Cain, vengeance shall be taken on him sevenfold. And the LORD set a mark upon Cain, lest any finding him should kill him.
What did this mean that vengeance shall be taken on him sevenfold?
This question is answered by most of the standard commentaries:
Ellicott:
Sevenfold.—Cain’s punishment was severe, because his crime was the result of bad and violent passions, but his life was not taken because the act was not premeditated. Murder was more than he had meant. But as any one killing him would mean murder, therefore the vengeance would be sevenfold: that is, complete, seven being the number of perfection. Others, however, consider that Cain’s life was under a religious safeguard, seven being the sacred number of creation. In this we have the germ of the merciful law which set cities of refuge apart for the involuntary manslayer.
Benson:
Genesis 4:15. Whosoever slayeth Cain, &c. — God having said, in Cain’s case, Vengeance is mine, I will repay, it had been a daring usurpation for any man to take the sword out of God’s hand. And the Lord set a mark upon Cain — To distinguish him from the rest of mankind. What the mark was, God has not told us: therefore the conjectures of men are vain.
Barnes:
The reply of the Lord is suited to quell the troubled breast of Cain. "Therefore." Because thy fears of what thou deservest go beyond what it is my purpose to permit, I give thee assurance of freedom from personal violence. "To be avenged seven-fold" is to be avenged fully. Cain will no doubt receive even-handed justice from the Almighty. The assurance given to Cain is a sign, the nature of which is not further specified.
This approach, used by God with Cain, is consistent with the prayer of the psalmist in Ps 79:12:
Pay back into the laps of our neighbors sevenfold the reproach they hurled at You, O Lord.
This is also consistent with the NT principle that:
Rom 12:19 - Beloved, never avenge yourselves, but leave it to the wrath of God, for it is written, “Vengeance is mine, I will repay, says the Lord.” (see also Heb 10:30 and Deut 32:35)
There is a subtle logical conflict that worth a thought. Let's first read Genesis 4:12-14
12 When you work the ground, it will no longer yield its crops for you. You will be a restless wanderer on the earth.”
13 Cain said to the Lord, “My punishment is more than I can bear.
14 Today you are driving me from the land, and I will be hidden from your presence; I will be a restless wanderer on the earth, and whoever finds me will kill me.” (NIV)
The punishment Cain received from the Lord was the ground would not yield enough food to him. But Cain concerned more that he would be killed.
Now we had the arguments;
Cain and his descendant were all gone after the flood, but why would the scripture kept his genealogy until his 7th generation - Tubal-Cain?
I have the following extracted from Wikipedia
According to Rashi, Tubal-cain's name literally means "Cain's-Spices", with the Hebrew word Tū́ḇal (תובל) deriving from the word Tū́ḇlin (תבלין) meaning spices. Rashi states that he was named this, because he "seasoned and improved the work of Cain". In other words, because he was a blacksmith, who helped to make weapons which could be used to kill more efficiently, he invokes his ancestor Cain's sin of murder. Furthermore according to Tanhuma bar Abba, one day, Tubal-cain and his father, Lamech, were hunting together with Tubal-cain serving as an aid for his blind father. In the distance is Cain who Lamech believes to be an animal. He checks with Tubal-cain to see if it is an animal, but Tubal-cain deceives his father, and lets him shoot and kill his forefather Cain, possibly because of Tubal-cain's blood lust. When Lamech realizes what he has done, he throws his hands up in a fit of mourning, accidentally killing his son Tubal-cain. However Genesis Rabbah disagrees with this narrative.
Whether the above interpretation is true or not, but one is certain to me, when Lamech said to his wives, in Genesis 4:24
24 If Cain is avenged seven times, then Lamech seventy-seven times. (NIV)
It echoed to the Lord said in Genesis 6:5
5 The Lord saw how great the wickedness of the human race had become on the earth, and that every inclination of the thoughts of the human heart was only evil all the time. (NIV)
Hence came forth the Flood to create a new world.
