Isaiah 45:6 That they may know from the rising of the sun, and from the west, that there is none beside me. I am the LORD, and there is none else.
He wants them to know from the east to the west that He is the only God that exists. A clear idea that Isaiah knew that God wanted His name and glory proclaimed to the world. A messenger is being sent forth speaking of John the Baptist but in the first application it seems that the God who carried about Nineveh cared about the world. He is God, the creator. He desires that men know Him and worship Him.