Isaiah 43:10-19 is controlled by the opening declaration of God: “You are my witnesses…”  The sermon is controlled by the reason for our status as witnesses/servants: “…that you may know and believe me and understand that I am he” (cf. Isaiah 43:10).  This logic should catch us all off guard for a moment.  We don’t expect this reason for being witnesses.  We expect to be witnesses for God so that others might know Him.  Instead, we learn that God has allowed us to experience His transforming power so that we might know Him.  It’s not, then, about productivity, but about intimacy.  The rest of the section highlights the unique status God has among the gods.  We Christians are the ones who say to the world, “God is who He says He is and can do for you what He’s done for me–save.”  That implies, of course, that we are experiencing His transforming power.  Notice the question in Isaiah 43:19.  Surely, we are a people who perceive the “new thing” God is doing.