A biased account would have ascribed nothing good to Cain. The truth is more complex: God was to make much use of Cainite techniques for his people, from the semi-nomadic discipline itself (20) to the civilized arts and crafts. The phrase he was the father of all such acknowledges the debt and prepares us to accept for ourselves a similar indebtedness to secular enterprise The family of Lamech could handle its environment but not itself. The attempt to improve on God’s marriage ordinance (19; cf. 2:24) set a disastrous precedent, on which the rest of Genesis is comment enough; and the immediate conversion of metal-working to weapon-making is equally ominous. Cain’s family is a microcosm: its pattern of technical prowess and moral failure is that of humanity. Polygamy – observed not condemned. “mercy”.
Lamech’s song reveals the swift progress of sin. Where Cain had succumbed to it (7) Lamech exults in it; where Cain had sought protection (14, 15) Lamech looks round for provocation: the savage disproportion of killing a mere lad for a mere wound is the whole point of his boast (cf. 24). On this note of bravado the family disappears from the story. –Kidner