John Calvin Commentary Isaiah 30:28

"and his breath is as an overflowing stream, that reacheth even unto the neck, to sift the nations with the sieve of destruction: and a bridle that causeth to err [shall be] in the jaws of the peoples." — Isaiah 30:28 (ASV)

And his Spirit. He proceeds with the threat he had begun to utter, namely, that the Church will indeed be chastised, but that the Assyrians will utterly perish. For he says that they will be plunged into the deep by the 'Spirit' of God, or rather, that the 'Spirit' himself is like a deep torrent that will swallow them up. Others translate רוּחַ (rūăch) as 'blowing,' and think that the allusion is to a storm or violent wind.

And with a useless sieve. The next metaphor used is that of a 'sieve,' which is very frequent in Scripture (Matthew 3:12). He says that he will shake the Assyrians with a sieve, in order to thresh and scatter them; and therefore he calls it 'the sieve of vanity,' that is, a useless sieve, intended not to preserve but to destroy. For, in another sense, the Lord is accustomed to 'sift' his own people also, so as to gather them like good grain into the barn.

And a bridle causing to err. The third metaphor is that of a 'bridle,' by which the Lord continually restrains the pride and rebelliousness of wicked men, and, in a word, shows that he is their Judge. True, indeed, the Lord commonly restrains and subdues his own people by a 'bridle,' but it is in order to bring them to obedience; while, on the other hand, he restrains wicked men in such a manner as to cast them down headlong to destruction. This is what he means by the phrase 'causing to err.' As furious horses are driven about in all directions by their riders, and, the more they kick, are more violently struck and beaten, so the ungodly, when they are kept back, rush eagerly in the opposite direction, as it is beautifully described by David (Psalms 32:9).

The object of these metaphors is to show that we must not trifle with the Lord. For, although he may appear for a time to act differently, we will eventually know by experience the truth of what the Prophet says: that his 'breath' alone will be like a torrent to cast down the wicked, so that they may be suddenly overwhelmed.

Next, when he gives warning that the nations will be winnowed with 'a useless sieve,' we ought to fear that if the Lord finds in us nothing but chaff, he may throw us on the dunghill.

Lastly, we must observe the difference that exists between the children of God and the reprobate. For the Lord chastises both, but in different ways: the children of God, so that they may be purified and preserved; and the reprobate, so that they may be cast down headlong and destroyed.