John Calvin Commentary Isaiah 10:17

"And the light of Israel will be for a fire, and his Holy One for a flame; and it will burn and devour his thorns and his briers in one day." — Isaiah 10:17 (ASV)

And the light of Israel shall be for a fire. There is an elegant allusion to that burning by which he threatened that he would consume the Assyrians. In fire there are two things: light and heat. As the Lord consumes the enemies by his heat, so he enlightens the godly by his light.

It is very customary that God is sometimes called a devouring fire (Deuteronomy 4:24; Deuteronomy 9:3; Hebrews 12:29), and sometimes, in a different point of view, he is called light (Isaiah 60:20; Micah 7:8), because his power produces contrary effects on the godly and the ungodly. When he shines on the godly, he imparts life and nourishment to them, but he consumes and destroys the ungodly.

In a word, while he threatens destruction to the Assyrians, he likewise brings comfort to the godly. He does so in two ways: first, they will see that God avenges the injuries they have received; and secondly, they will be cheered by his light and will thus receive a new life.

And his Holy One for a flame. He states plainly, and without a metaphor, what that light is when he adds his Holy One, so that a more lengthy exposition is unnecessary. The meaning is that he determines to protect that people whom he has chosen and whom he has separated from the rest of the nations to be his own special people.

And it shall devour its thorns and briers in one day. He now shows that the favor of God, which shines in Israel, will be like a fire to consume enemies. In one day means that he will burn them with a sudden and unexpected conflagration.

This denotes an uncommon and dreadful burning, which usually overtakes the wicked suddenly when they think that all is well with them, and that danger is far away. He next shows that, whatever defences they may employ, they will be like tinder, which, as soon as it is set on fire, will instantly be consumed.