What does Genesis 4:20 mean?

This section provides genealogies listing the important descendants of Cain. Ancient genealogies did not typically mention every single son or daughter. Rather, they focused on important figures, or simply listed the bloodline from one person to another. Even then, generations would sometimes be skipped to make the list shorter.

Lamech is the seventh generation from Adam, through Cain. One of his two wives, Adah, gives birth to a son called Jabal. We're told Jabal became the father of those who live in tents and have livestock. In other words, Jabal and his descendants likely became a nomadic people managing herds of several kinds of animals, perhaps including sheep, cattle, and others.

Later, we will see Lamech bragging about his murder of a younger man. The society which came from Cain was not only defiant towards God, but boldly and arrogantly sinful. As we move close to the story of the flood, this is crucial for realizing just how depraved mankind will become.