We know that the Gentiles are included in the New Covenant promises prophesied by Jeremiah in (C31:31-34). The easy answer is found in 1 Corinthians 11, where Paul taught this Gentile church about the Lord's Supper. Paul taught them about the New Testament which most assuredly was to them as children of God! But throughout the Old Testament scriptures, (all the way back to Abraham), there are promises that God would save a people from every nation, kindred, tribe, and tongue. In fact, in Hosea 1:10-2:1, God spoke of those whom He previously called "not my people" that they would be His people, and He would be their God. Hosea spoke of Israel, (the 10) tribes, and Paul used this passage (this promise) to show the inclusion of the Gentiles into what we might call spiritual Israel. Romans 9:22-26