Cain was born the oldest twin; same mother[Eve], different fathers. Satan is Cain's father. The LORD attempted to accept Cain, but Cain and his offering was Not accepted because of his rebellious genes that have a difficult time worshipping: because It has an insatiable appetite - to be worshipped.
"And Cain was very wroth." His countenance[facial expression]. After the initial training on how to present his "offering to the LORD, failing, then given a second opportunity to get it right: Cain murdered his half-brother Abel. This punishment: banishment -"cursed from the earth." Cain's inheritance of farming - revoked! A fugitive and a vagabond, for himself, and Children; forever.
"The LORD set a mark upon Cain"[upon - a sign], once identified, he and Children are to be left alone[Gen.4,Matt.13:30]. Cain left the Eden area, and dwelt in the land of Nod[wandering]; which is East. The Oriental Tribe that Cain Married and fathered is called Kajin [Strong's]. The word Kajin also = the first child.
This Tribe of Cain's descendants live out of tents and move around like Gypsies. They eventually show back up in 1Chronicles 2:55 as Scribes for the Tribe of Judah. The House of Rechab is also the same one in Jer.35. They refused communion with our LORD, because they are commanded Not to, by their father. Jer.35:11 explain how they ended up in Jerusalem while the Tribe of Judah was in bondage for 70 yrs. in Babylon.
The "Two-Baskets of Figs" that were shown[Jer.24] to the Prophet, took place after Judah had been carried away to Babylon. These Bad-Figs are the Children of Cain[Kenites]. The discernment is in the "Mark" of Cain: look at the fruit, works, productivity. The Thief[Satan], and His son Cain, and His Children are a specific Generation. Remember Jn.10:10 for their only objectives.