Isaiah 1:1 (NKJV)
1 The vision of Isaiah the son of Amoz, which he saw concerning Judah and Jerusalem in the days of Uzziah, Jotham, Ahaz, and Hezekiah, kings of Judah.
"While the vision concerns a specific city and nation in the eighth century BC, we shall see when we get to the beginning of chapter 2 that this is merely the vantage point from which the prophet looks out. The vision is in fact breathtaking in its scope, embracing all nations and reaching to the very end of time. Here is a vision which is bound to deliver us from spiritual myopia and small-mindedness if only we can grasp it, or, better still, allow it to grasp us." - Webb
And, of course, this teaches us as well that the promises of the Old Testament for future Israel are never about old Israel in the sense of a single ethnic group. Rather, as God works with that Israel He is teaching us about what He is doing and will do with the New Israel, the resurrected Israel, the Israel of God which is the church of Jesus Christ.
Isaiah's "Israel" is merely a vantage point for us to see the world and all of God's plans for it.