What did God require people to do in order to be restored and reconciled to Him?
God required people to do what He asked: bring a blood sacrifice, and He would accept them. Abel was accepted because he obeyed God's instruction; Cain rejected it. Reconciliation was conditional on obedience to God's stated requirement. That pattern shows restoration came only through the sacrifice God prescribed.
Les explains that God had offered a restoration and reconciliation if people would simply do what He asked: bring a blood sacrifice, and He would accept them. This was typified in Abel, who was accepted because he did what God told him to do, while Cain rejected it, rationalized it, and went his own way. After 2000 years of dealing patiently with those early people, God said He would do something different. He would take one man in whom He could find a particle of faith, one who would be obedient to what God told him, make him promises and covenants, bring a special race of people, and work a plan of salvation through that race. Once God revealed even the embryonic part of that plan of redemption, the devil kicked into high gear, which is why that special nation suffered so much.