What is the significance of Cain’s progeny and how they are described (Gen 4:17-24)?

First of all, they founded the first named city; note that cities, particularly cities of the east such as Babylon and Nineveh, were often associated with sin. Lamech was a murderer, so the iniquity did not leave the family. Another detail worth noting is that, if Jabal had been the original tent-dwelling nomadic herdsman—thus taking Abel’s place—then his ancestors, going back generations to Cain, must have been hunter-gatherers.