Jamieson, Fausset and Brown on Genesis 4:23-24

23-24. Lamech said unto his wives--This speech is in a poetical form, probably the fragment of an old poem, transmitted to the time of Moses. It seems to indicate that Lamech had slain a man in self-defense, and its drift is to assure his wives, by the preservation of Cain, that an unintentional homicide, as he was, could be in no danger.