Thank you my dear friend for this very good question. Before we get to the “seven fold” part, let me first give some background on this portion of Scripture, and review the issue with Cain which led up to the question of Genesis 4:15. As you know from reading Chapter 3, Adam and Eve had sinned by their lack of obedience to God’s commandment that of all the fruit trees of Eden, there was one that was not to be eaten of. They ate of it anyway, Eve being deceived by the serpent, and Adam receiving the fruit from his wife, even though he realized this was expressly forbidden of God (willful rebellion). The ground was cursed due to their sin, and each had their punishments related. But what can cover sin? We read in Genesis 3:21, “Unto Adam also and to his wife did the LORD God make coats of skins, and clothed them”. In the McDonald Commentary on Genesis 3, we get some very good insight: “…tunics of skin were provided by God through the death of an animal. This pictures the robe of righteousness which is provided for guilty sinners through the shed blood of the Lamb of God, made available to us on the basis of faith”.

I am not sure exactly how God imparted the knowledge of the need for blood to cover their sins, but apparently this was made clear to Adam and Eve and their children as we see Abel bringing a blood offering before the Lord, which was accepted, while Cain’s vegetable and fruit offering was not accepted of the LORD. Abel therefore apparently understood what Cain did not, that he was a sinner, and that only a blood offering could be a sin offering. However, instead of correcting his ways and bringing a proper offering, Cain became angry and very jealous of Abel. This anger alone was a sin. (Read Matthew 5:21-22). In Genesis 4:6-7, we read, “And the LORD said unto Cain, Why art thou wroth? and why is thy countenance fallen? If thou doest well, shalt thou not be accepted? and if thou doest not well, sin lieth at the door. And unto thee shall be his desire, and thou shalt rule over him”. God sought to warn Cain about how to overcome this sin of jealousy and hate, and how to be right with God through bringing a proper sacrifice; but Cain did not listen to God, and in verse 8, he rose up and slew Abel. Later, when confronted by God about what he had done to his brother, Cain gave a flippant response to God, showing that Cain had no real consciousness of sin. Cain did not confess his sin, nor did he seek God’s mercy for what he had done. His only concern was what might happen to him when in punishment, God drove him away. He instead complained that others might take vengeance on him for the murder of Abel, given that God had driven him out into the world, to live as best he could without guidance or the fellowship of God. We read in genesis 4:14-15, “Behold, Thou hast driven me out this day from the face of the earth; and from Thy face shall I be hid; and I shall be a fugitive and a vagabond in the earth; and it shall come to pass, that every one that findeth me shall slay me. 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.

Now, as to your question regarding the sevenfold vengeance on anyone who might kill Cain, I believe this to be God’s mercy on Cain, that even though he had greatly sinned and did not repent and offer a blood offering, since Cain was driven out before God, the LORD would not allow anyone to seek vengeance since judgement had been executed already, and vengeance belongs to God only (Deuteronomy 32:35, “To Me belongeth vengeance and recompense…”)  the judgement of Cain, being thus driven out before the face of God, and losing any fellowship with God, was quite severe, and no one else was to add to it as Cain was to live out his days in exile, without God’s guidance. Thus, Cain received a mark, and anyone who might dare to kill Cain would be subject to a “sevenfold” judgment by God. The term “seven-fold” refers, I believe, to the magnitude and completeness of God’s punishment of anyone who dared to interfere with God’s righteous judgment of Cain. The cost to anyone daring to punish Cain further would be seven times the severity of judgment which might be anticipated of God, thus causing any potential avenger of Abel to fear to lay a hand on Cain, and thus protecting Cain’s life and preserving his posterity.

Now, considering this sevenfold judgment on any avenger who might harm Cain, we learn about another situation with a son of Cain, Lamech, in Genesis 4:23-24: “And Lamech said unto his wives, Adah and Zillah, Hear my voice; ye wives of Lamech, hearken unto my speech: for I have slain a man to my wounding, and a young man to my hurt. If Cain shall be avenged sevenfold, truly Lamech seventy and sevenfold.”

It sounds as though Lamech sinned also in having 2 wives, and he also killed a man, I presume, in self-defense. I don’t know that Lamech offered a sin offering either, but he certainly considered his killing of a man to be a much less egregious a matter than Cain’s murder of his brother Abel, the latter being done without a cause. Therefore, Lamech felt that he, if killed by someone in vengeance, should be avenged by God with a 10 times greater response than that afforded to Cain. This was Lamech’s reasoning only, and it appears to me that Lamech had no real consciousness of sin either but was only worried about the potential consequences of having killed, even if in self-defense.

My dear friend, I hope this response to your question is helpful to you.  My prayers for you come with this response, and I truly hope that as you read this, you can say with certainty that your sins are forgiven through faith in the shed blood of our Lord Jesus Christ, whose blood alone can take away sins as we read in Hebrews 10:4, “For it is not possible that the blood of bulls and of goats should take away sins”. We read further in Hebrews 10:10 “…we are sanctified through the offering of the body of Jesus Christ once for all”. Have you trusted in the Lord Jesus as your Savior? If not, consider the words of our Lord Jesus in John 5:24: “Verily, verily, I say unto you, He that heareth My word, and believeth on Him that sent Me, hath everlasting life, and shall not come into condemnation; but is passed from death unto life”.  (488.2)  (SF)