Jesus is both the Israel of God and God Himself, for the same reason He is both the mediator between God and man and God Himself:
Hos 11:1 When Israel was a child, then I loved him, and called my son out of Egypt.
Mat_2:15 And was there until the death of Herod: that it might be fulfilled which was spoken of the Lord by the prophet, saying, Out of Egypt have I called my son.
Jesus said, “Salvation is of the Jews.” Acts 1:8.