Isaiah 31:6 (NKJV)
6 Return to Him against whom the children of Israel have deeply revolted.
"Repentance is radical. It is not just giving up this or that sin, but a complete turnabout in our stance towards God, and it goes right to the root of our sinfulness." - Webb, p133.
In that repentance, God promises something wonderful - vv8-9 declare that God will deal with Assyria, destroying them "by a sword not of man." this from the LORD, "Whose fire is in Zion and whose furnace is in Jerusalem."
"In view of all this (chapters 29-31), the expression "in that day" (v7) must be allowed to point beyond the events of 701 BC to something more distant and more perfect, as it so often does elsewhere in the book. There was no perfect repentance or perfect salvation in 701. But God's gracious goodness to his people when they cried out to him then was a foretaste of something far greater and more glorious..." - Webb, p134.
Repentance can sound like such an angry word "Repent!" But it is actually a word of release and salvation. "Return to me!" "I am Your deliverance!" "Be free of those dead and lying idols!"