In several verses he says "Listen to me..." That is powerful! Pay attention. Listen up. This is important.
In the Gospels we often hear Jesus say "Verily" or "Truly" in the same way. Highlight this. Put a star here.
When he calls the listeners this way, he is not addressing the nations, but the faithful. He is calling them to remember where they came from and to recall their heritage. He wants them to return to the place they once occupied. They are in exile. They are experiencing the punishment for their sins of idolatry. But they will be restored. The cup of the Lord's wrath was delivered to Judah and Jerusalem, but the promise is that now it has been drained, and they are to return to their land, and it will be restored to plenty.
This was written to the nation, but maybe it applies to individuals too. Have you felt the crush of God's wrath on your behavior and your sin? Have you sought him in long dark nights? He calls for you to awake and enter into his gladness and joy. After the punishment is completed, the return to his grace is accompanied by singing.
Read the verses of Isaiah 51. If you are not at the time of rejoicing yet, hold on. It is coming!
References are from the NIV.