John Calvin Commentary Isaiah 33:11

"Ye shall conceive chaff, ye shall bring forth stubble: your breath is a fire that shall devour you." — Isaiah 33:11 (ASV)

You shall conceive chaff. He now addresses his discourse to the enemies of the Church, whose insolence, he says, is foolish and futile; for when God has brilliantly displayed his power, they will know that their efforts will be fruitless, and that they will accomplish nothing, even though they are leagued together in vast crowds. The Lord laughs at their madness, in thinking that everything is in their power, when he can instantly, by the slightest expression of his will, restrain and destroy them, though they may be defended by a very powerful army.

It is customary in the Scriptures to use the word conceptions for indicating the designs and efforts of men (Job 15:35; Psalms 7:14; Isaiah 26:17; Isaiah 59:4). The metaphor is taken from pregnant women. Men are said to “conceive” and to “bring forth” when they attempt anything; but he declares that their “conception” will be fruitless, and that they will also “bring forth” to no avail, for whatever they undertake will be unsuccessful. There is nothing, therefore, in the brilliant military forces of our adversaries that should alarm us; for, although God may permit them for a time to bustle, and toil, and rage, yet God will eventually turn into “chaff” all their rash and daring attempts. Let us learn that what Isaiah foretold about Sennacherib relates to all the adversaries of believers and of the Church.

The fire of your breath shall devour you. That they “shall be devoured by the fire of their breath” is usually explained to mean, “Your breath, like fire, shall devour you.” But that is an unsuitable and even absurd comparison, and the true meaning readily suggests itself, “The fire kindled by your breath shall devour you.” We commonly kindle a fire by blowing, and therefore he declares, that the fire which wicked men have blown by their wicked contrivances will be destructive to them, because it will consume them. It is the same statement which is often conveyed by a variety of metaphors in Scripture.

They shall fall into the pit which they have digged. They are entangled in a net which they had prepared for others. The sword which they had drawn hath entered into their own bowels. Their arrow hath been turned back to pierce their own hearts. (Psalms 7:15; Psalms 37:15; Psalms 57:6).

Thus the Prophet shows that the wicked tyrant who laid waste Judea and besieged Jerusalem with a numerous army, and all others who similarly are adversaries of the Church, bring down destruction on themselves, and will in the end be destroyed; and, in short, that they will be consumed by that “fire” which they have kindled.