The darkness is not so great now as in Isa. 5:30 because IMMANUEL is here, as light, when Christ is introduced as the One who is to have the kingdom of David.
The prophet's vision goes on now to the increasing joy of God's people, the oppressor gone, and Jehovah on the throne, increasing in power until the whole world is subdued.
In verse 8 of this chapter a new subject is begun. (This ends the parenthesis referred to in comments on chapter 6.) The prophet takes us back to the time when, after no response from the nation, He declares that He will "cut off from Israel head and tail, branch and rush, in one day. The ancient and honorable, he is the head; and the prophet that teacheth lies (false prophet), he is the tail." There can be no peace for the nation until Jehovah, having removed all internal and external enemies, takes the throne to reign in righteousness.