The imagery of the captive returns, and the Lord makes it clear that the captivity is one of the spirit, and one which Israel may remove by simply awakening to the word of the Lord.
Message to Jacob's audience: Jacob will make an explicit analysis of the meaning of the redemption from captivity in verse 9, and correctly will take the Lord's eternal view and see the Savior's mission as the ultimate redemption. However, it is also quite likely that this passage from Isaiah would continue to reverberate in more immediate ways for the Nephites.
Israel's historical problem with its bellicose neighbors is shown by Isaiah to be a result of their spiritual sleep. The Nephites, while maintaining victory in their skirmishes to this point, yet must have plainly seen the possibilities of captivity. The reminder that such may be avoided through righteousness is a subtheme that they surely would have understood. That subtheme of preservation through righteousness, and captivity through wickedness becomes a liet-motif for the entire Book of Mormon narrative.