Gen3: The serpent deceived the woman. She and Adam ate from the tree. The ground was cursed, and God sent Adam and Eve out of the garden.
Why did God not accept Cain’s offering? Because there was no blood shed which is an appropriate sacrifice sins. Cain only brought produce of the ground, indicating that he had to work for his forgiveness. The point is that Cain tried to work for his forgiveness or salvation from his sins and God never accepts works, and works cannot ever be accepted for sin offerings because we are always saved by grace and never by works (Eph 2:8-9).
Adam and Eve had 2 sons named Cain and Abel. Abel grew to become a herdsman who worked with animals while Cain became a Farmer who tilled soil. One day when it was time to offer their sacrifices to God, Cain offered fruits which represented his works instead of a lamb while Abel sacrificed the best lamb that he had. God consumed Abel’s offering but not Cains.
Cain become angry towards his brother, murders him and attempts to hide it from God. God asking where Cain’s brother was, hears Abel’s blood crying from the soil and curses Cain so that the ground will never produce it’s best. Cain being scared of being murdered is protected by God’s grace and mercy when God puts a covenant over Cain that if anyone was to murder him, they would suffer 7 times over. God sent Cain was sent away.