New Defender's Study Bible Notes
4:19 two wives. Lamech is the first recorded rebel against the divine command of monogamous marriage. It is probable that Adam died during Lamech’s time (by comparison with the chronological data in the Sethitic line) and the Cainites thenceforth became more openly rebellious against God.
4:19 Zillah. “Adah” apparently means “ornament” and “Zillah” means “shade.” Lamech’s motivation in taking two wives may have been partially physical lust and partially the desire to establish a large clan in the increasingly violent antediluvian society.