John Calvin Commentary Isaiah 9:18

"For wickedness burneth as the fire; it devoureth the briers and thorns; yea, it kindleth in the thickets of the forest, and they roll upward in a column of smoke." — Isaiah 9:18 (ASV)

For wickedness burneth as the fire. The Prophet attacks the wicked, who are accustomed to defend themselves by blaming God. They either use evasions to convince themselves that they are innocent or, when convicted, they still downplay their guilt, as if God's severity were excessive.

Certainly, they never acknowledge that God is just in punishing them until they are compelled to do so; and even if they do not dare to excuse themselves publicly, they still fret and murmur.

To repress such insolence, the Prophet compares the calamities to burning, but shows that human wickedness is the wood and fuel by which God's anger is kindled. It is as if he had said, “All exclaim and loudly complain that God’s wrath burns violently, yet they do not consider that their own sins are the fans by which it is inflamed, that these sins supply the fuel, and that they themselves are consumed by the inward fire of their crimes.”

It shall devour the briers and thorns. The meaning is that this flame will seize every part of Judea. Two things are expressed here: that the punishment of sin proceeds from God's judgment, and yet that the blame lies with the sinners themselves, so that they may not protest to God as if He had treated them cruelly.

There is a beautiful gradation, for we perceive that it usually happens that a fire, kindled in the lowest part of any place, gathers strength by degrees, spreads wider and wider, and ascends to the higher parts. Such will be the wrath of God, for Isaiah shows that it does not seize the wicked all at once, but is gradually kindled until it utterly destroys them.

At first the Lord proceeds gently, but if a light chastisement produces no good effect, He increases and doubles the punishment. If He sees that we are obstinate, His wrath burns to the utmost, so as to destroy us altogether and consume us like a thick forest.

Lastly, as the Prophets elsewhere declare, we will be like chaff and straw as soon as the wrath of God is kindled (Psalms 83:14; Isaiah 5:24; Isaiah 33:11; Isaiah 40:24; Isaiah 41:2; Isaiah 47:14).