What did God tell Israel He would give them?
God told Israel He would give them the Law, the priesthood, and the whole system of sacrificial worship. At Mount Sinai, through Moses, He was about to give them the covenant of Law, promising that if they obeyed His voice and kept His covenant, they would be a peculiar treasure above all people.
Les explains that this was something that had never happened before: God told the nation of Israel He would give them the Law, the priesthood, and the entire system of sacrificial worship. The purpose was to make them aware of God's holiness, His sovereignty, and that He was preparing them for a future role amid the pagan idolatry around them. At Exodus 19, as Israel encamped at the base of the mountain and Moses talked with God, God said that if they obeyed His voice and kept His covenant—the covenant of Law He was about to give—they would be a peculiar treasure unto Him above all people. This lifted Israel out of the mainstream of humanity and put them into covenant relationship as God's favored, chosen people.