What, specifically, does Isaiah's prophecy proclaim about deliverance for the people of God?

First, it is a proclamation of good news for the poor. The "poor" are those who have been impoverished in any way by captivity of any kind. They are those who have been oppressed by the devil and held down in circumstances less abundant than that which God intended for His people. The poor shall experience release from their sorry situation.

Second, it is a proclamation that the brokenhearted will be bound up. The "brokenhearted" are those who have been deeply affected by their captive situation. They are those who are sorry for their sins. The Lord will bind up, that is, console their broken hearts (see Psalm 34:18).

Third, it is a proclamation of freedom of freedom for the captives. The "captives" are those who have been enslaved in any sense of the term. They are those who have been held back by the devil from achieving that which God wants them to achieve in life. The Lord will set them free.

Finally, it is a proclamation of release from darkness for the prisoners. The "prisoners" are those who have been kept from seeing the true nature of their captivity. They are those who have been kept in the dark by the devil. The Lord will release them from darkness into His glorious light (see 1 Peter 2:9).

In Christ, the Lord is enriching, consoling, freeing, and enlightening you. And His work in you has really only just begun (see Philippians 1:6)