Then Isaiah expands on the promise. Not only will they be rescued, but also everybody will know about it-- "her salvation like a burning torch."
OTOH, some commentators believe that the promise not to keep silent and not to rest are Isaiah's, rather than his proclaiming God's words.
Under the heading, troubling or reassuring?, no mention is made of their need to repent, or even to ask for, deliverance.
Lectio Divina: How precious is your steadfast love, O God! All people may take refuge in the shadow of your wings (Psalm 36:7).