What was the purpose of Jesus' first advent to Israel?
The purpose of Jesus' first advent to Israel was to appear as the promised King, the final son of David, in fulfillment of the covenants and promises God made to the nation. He came to be that promised King according to the covenants, presenting Himself to Israel as the promised King.
Les teaches that the family tree comes all the way down through history until Joseph on one side and Mary on the other, and Christ is the last possible son of David that could be the King. He makes His appearance to the nation of Israel. That, Les says, is the whole idea of His first advent—that He came to be that promised King according to the covenants. Paul confirms this in verses 3 and 4, speaking of his kinsmen according to the flesh, who are Israelites, to whom pertain the adoption, the glory, the covenants, the giving of the law, the service of God, and the promises. God had promised the nation over and over.