Could Israel have evangelized the Gentiles in the Old Testament?
Yes. Had Israel remained faithful, the nation could have been a kingdom of priests and a light to the Gentiles, evangelizing them and bringing them to a knowledge of Jehovah. The Old Testament program allowed for this, but Israel did not fulfill it; the potential was real but hypothetical.
Les explains that God had not lost sight of the Gentile river of humanity. From Abraham until into the New Testament, God was looking at the Jew only, with exceptions, but the whole program was laid out so Israel could have evangelized the Gentiles and brought them to a knowledge of Jehovah. They could have been a nation and a kingdom of priests. Les emphasizes "could have" because they did not, though hypothetically it could have happened. The quoted passage says God would give Israel as a light to the Gentiles and salvation to the end of the earth. In Isaiah 59, the Redeemer comes to Zion—Jerusalem—and to those who turn from transgression in Jacob, meaning Israel's spiritual climate had to be 100 percent believers. Peter later says, "every one of you."