Cain and Able were twins; same mother, different fathers. They were both taught of the LORD, and shown the correct way. Cain was to be a farmer; just like the-man-Adam. Able was a Shepherd. An Offering was important enough that it was taught by the Creator Himself, and accepted, or rejected based on The, Standard!
The Standard was Obedience and Faith. Follow the Instructions: bring fourth the best, from the increase: via Faith, this produces more. Cain's Offering was rejected because he replaced Obedience, with rebellion, and it lack Faith.
Cain went on to get rid of the Standard by murdering his brother; then for 6,000 yrs. switch places with his righteous brother Abel. His children even today practice religion[to return to bondage] - just as Cain attempted with his Offering.
Immanuel-Christ-Jesus constantly called out a specific nation as "Hypocrites"= In the Greek: play actors. Matt.23:2 "The Scribes and Pharisees sit [have taken] in Moses seat". Moses was of the Tribe of Levi; Priest, and Judge. These play-actors required of others, but refuse for themselves.
Matt.23:31 Christ-Jesus states that these are witnesses against themselves, that they are the Children of them which killed the prophets. Matt.23:35 is very clear and specific as to who this nation is. Cain pulled a fast one years ago: it continues today with religious-leaders being the deceptive-water-boys for this blind-nation.