A form of argumentation that was used by St. Athanasius to defend Jesus’ Messiahship against the Jews was by appealing to the conversion of Gentiles; who began to forsake their idols and acknowledge the true God of Israel. This was a fulfillment of Old Testament prophecy, which morally held Jews to accept the undeniable evidence that Jesus is the Christ; as the scriptures are held to be authoritative by both Jews and Christians alike.
In his words:
“… when they see even heathens deserting their idols, and placing their hope, through Christ, on the God of Israel, do they deny Christ, Who was born of the root of Jesse after the flesh and henceforth is King? For if the nations were worshipping some other god, and not confessing the God of Abraham and Isaac and Jacob and Moses, then, once more, they would be doing well in alleging that God had not come. But if the Gentiles are honoring the same God that gave the law to Moses and made the promise to Abraham, and Whose word the Jews dishonored, why are they ignorant, or rather why do they choose to ignore, that the Lord foretold by the Scriptures has shone forth upon the world, and appeared to it in bodily form?”
~ On the Incarnation, CHAPTER VI.
Faith Unto Ages 