Isaiah 9:1 is structured around a contrast between the “beginning time” and the “after time.” In the beginning time, Yahweh treats the land of Zebulun and Naphtali “lightly,” but in the after time, He will cause it to be heavy, glorious.

This movement from light to heavy is, as verse 2 makes plain, also a movement from darkness and gloom to light. Darkness is light, a sign of contempt; light is glory.

And this is of course the movement of creation, from primordial darkness to the creation of light, from evening to morning, from less glory to greater glory.