What does the Bible say about the conversion of Gentiles?

Isaiah 66 speaks of God's promise to set a sign among the Gentiles, indicating that the gospel will extend beyond Israel. This prophecy fulfilled in the New Testament shows how God calls a people from all nations, not merely through ethnic ties but through the spiritual reality of being part of true Israel or the Church. It underscores the sovereign grace of God in seeking out those who are considered 'far off' and bringing them into His fold, thus demonstrating His mercy and the breadth of the gospel's reach.