That’s a great question!  This Lamech was a direct descendent of Cain as we read in Genesis 4:16-18, “And Cain went out from the presence of the LORD, and dwelt in the land of Nod, on the east of Eden. And CAIN knew his wife; and she conceived, and bare Enoch: and he builded a city, and called the name of the city, after the name of his son, Enoch. And unto Enoch was born Irad: and Irad begat Mehujael: and Mehujael begat Methusael: and Methusael begat LAMECH.”  Cain, of course, was the firstborn son of Adam and Eve.  When we think of Cain as being the first man ever born (Adam and Eve were created), we realize that the first man born was also the first murderer.  He murdered his brother, Abel, when the Lord rejected Cain’s sacrifice, but accepted Abel’s sacrifice.

Let’s read Genesis 4:19, “And Lamech took unto him two wives: the name of the one was Adah, and the name of the other Zillah.”  Now let’s read verses 23-24, ““Adah and Zillah, hear my voice; wives of Lamech, listen to my speech! For I have killed a man for wounding me, even a young man for hurting me. If Cain shall be avenged sevenfold, then Lamech seventy-sevenfold.”” (NKJV).  From these two verses, we realize that the life of Lamech was the Bible’s first mention of polygamy and he continued in Cain’s disobedient and murderous ways. 

Who was this man that Lamech killed?  I have read differing speculations, but since the Bible does not tell us who this man was, I believe we can still get the lesson of this portion without knowing the identity of this murder victim.  In Lamech’s boastful words to his wives, he is comparing himself to Cain.  While Cain murdered his brother, Abel, deliberately and without provocation, Lamech points out that he killed a man in self-defense.  This young man had hurt Lamech, wounding him. 

“IF CAIN SHALL BE AVENGED SEVENFOLD, THEN LAMECH SEVENTY-SEVENFOLD” – We know the Lord had promised a sevenfold promise of revenge to any who would harm Cain.  We read in Genesis 4:13-15, “And Cain said unto the LORD, My punishment is greater than I can bear. 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.” 

Lamech reasoned that if the Lord promised a sevenfold revenge on any who would harm Cain, a deliberate murderer, surely He would avenge Lamech’s death seventy-sevenfold to any who would harm him, since it came from self-defense.  Perhaps it was because of Lamech’s killing of a man that his wives were worried, thinking the relatives of the deceased man would seek to kill him in return.  In order to calm their fears, he makes this speech, in which he attempts to prove that there was no room for fear on this account.  (CC)  (736.2)