What did God promise Israel if they obeyed His voice and kept His covenant?

God promised that if Israel obeyed His voice and kept the covenant He was about to give, they would become His peculiar treasure above all people. This set them apart from the nations, lifting them out of humanity's mainstream into covenant relationship as God's favored, chosen people.

Les explains that at Mount Sinai, Moses was up talking with God while the children of Israel encamped at the base of the mountain. God told Moses that if they would indeed obey His voice and keep the covenant of Law He was about to give, then they would be a peculiar treasure unto Him above all people. This lifted Israel out of the mainstream of humanity and placed them into covenant relationship as God's favored, chosen people, distinct even while the whole world was steeped in idolatry.

Exodus 19:5

Now therefore, if ye will obey my voice indeed, and keep my covenant, then ye shall be a peculiar treasure unto me above all people: for all the earth is mine:

What covenant was God about to give Israel at Mount Sinai?

At Mount Sinai, God was about to give Israel the covenant of Law, encompassing the Law, priesthood, and sacrificial worship system. This covenant would make them aware of God's holiness and sovereignty and prepare them for a future role amid surrounding pagan idolatry.