“It brings clarity, creates warmth, and provides power. Our need for light is often felt most in the middle of our literal or metaphysical darkest night, which is right where this verse begins. Isaiah is speaking to the people of God, who in their time of need chose to look to other nations for salvation rather than to Yahweh. The outcome of their choice was total devastation. The temple is destroyed, their nation is disbanded, and they are exiled to foreign countries.”
https://www.rzim.org/read/a-slice-of-infinity/light-changes-everything
One Day at a Time 