What was required for early people to be accepted by God?
For early people, acceptance by God required obedience to what He asked: specifically, bringing a blood sacrifice. God offered restoration and reconciliation on that condition, promising to accept them. Abel was accepted because he did what God told him to do, while Cain rejected that requirement and rationalized going his own way.
Les explains that God had offered restoration and reconciliation to early people if they would simply do what He asked: bring a blood sacrifice, and He would accept them. Abel is the example, because Abel was accepted by doing what God told him to do. Cain rejected it, rationalized it, and thought he would go his own way. Les notes that after about 2000 years of God dealing patiently with those early people, God then turned to one man of faith and made promises and covenants through him.