What was the Gentiles' relationship to Israel's God in the Old Testament?
In the Old Testament, Gentiles were never reckoned to have any relationship with Israel's God. They were outside that covenant connection; God had not called them as His people. Only later, through the apostle Paul's gospel, does God call out a people from among the Gentiles to be called children of the living God.
Les explains that in the Old Testament the Gentiles were never reckoned to have anything to do with Israel's God. They had no covenant relationship with Him, while Israel did. But now God has called out a people from among the Gentiles, and they are called the children of the living God. Les connects this to Romans 9:25-26 and notes that after this age, God will turn back to His covenant people, Israel. This called-out group is the Body of Christ, enjoying a position even Israel will never attain.
As he saith also in Osee, I will call them my people, which were not my people; and her beloved, which was not beloved.