The phrase "light of Israel" refers to Yahweh. It is unclear whether Yahweh or Isaiah is speaking. Alternate translation: "I, Yahweh, the light of Israel, will become like a fire, able to destroy everyone that does not honor me" (See: [[rc://en/ta/man/translate/figs-metaphor]])
"The fire will burn and devour the king of Assyria's thorns and briars." The speaker compares the king of Assyria's army to thorns and briers. This emphasizes how easily God will destroy them. Alternate translation: "I will destroy the Assyrians like a fire burning thorns and briers" (See: [[rc://en/ta/man/translate/figs-metaphor]])
The words "briers" and "thorns" both refer to useless, thorny plants; they can be translated using one expression. See how you translated these words in [Isaiah 7:23](../07/23.md). Alternate translation: "thorn bushes" (See: [[rc://en/ta/man/translate/figs-doublet]])