Here’s some encouraging thoughts from Alec Motyer, commenting on these verses:

Nevertheless the gloom will not be upon her who is distressed,
As when at first He lightly esteemed
The land of Zebulun and the land of Naphtali,
And afterward more heavily oppressed her,
By the way of the sea, beyond the Jordan,
In Galilee of the Gentiles.
The people who walked in darkness Have seen a great light;
Those who dwelt in the land of the shadow of death,
Upon them a light has shined.
(Isaiah 9:1-2)

Motyer writes:

As always, the people of God must decide what reading of their experiences they will live by. Are they to look at the darkness, the hopelessness, the dreams shattered and conclude that God has forgotten them? Or are they to recall his past mercies, to remember his present promises, and to make great affirmations of faith?

Isaiah insists here that hope is a present reality, part of the constitution of the “now.”

The darkness is true, but not the whole truth, and certainly not the fundamental truth.