The Lamech Principle

Genesis 4:24 - If Cain is avenged sevenfold, Then Lamech seventy-sevenfold."

A similar development, evidently, takes place in the nations outside the people of God. Lamech the descendant of Cain sings a song of vengeance in Gen 4:23f. As family head, he sings to his two wives about how he will execute vengeance for bloodshed. Unlike the simple reciprocity implied in Gen 9:6 and in the Mosaic law of talion (Exod 21:23-25), Lamech boasts that he will avenge seventy-seven times! “Family justice” indeed, but exaggerated far beyond anything our God would recognize as just.
16 Then Cain went out from the presence of the LORD and dwelt in the land of Nod on the east of Eden. 17 And Cain knew his wife, and she conceived and bore Enoch. And he built a city, and called the name of the city after the name of his son—Enoch. 18 To Enoch was born Irad; and Irad begot Mehujael, and Mehujael begot Methushael, and Methushael begot Lamech.
19 Then Lamech took for himself two wives: the name of one was Adah, and the name of the second was Zillah. 20 And Adah bore Jabal. He was the father of those who dwell in tents and have livestock. 21 His brother’s name was Jubal. He was the father of all those who play the harp and flute. 22 And as for Zillah, she also bore Tubal-Cain, an instructor of every craftsman in bronze and iron. And the sister of Tubal-Cain was Naamah.
23 Then Lamech said to his wives:
      “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.

 24 If Cain shall be avenged sevenfold,
      Then Lamech seventy-sevenfold.”