John Calvin Commentary Isaiah 17:12

"Ah, the uproar of many peoples, that roar like the roaring of the seas; and the rushing of nations, that rush like the rushing of mighty waters!" — Isaiah 17:12 (ASV)

Alas for the multitude! Some translate this as 'Woe,' making it denote condemnation. Sometimes, as we have seen elsewhere, it is used to call out to a person; but on this occasion, I rather think that it signifies sorrow, for he groans because of the calamity he foresees will happen to Israel, and he does so either out of brotherly affection or so that the prophecy may make a more powerful impression on the minds of a sluggish and lazy people.

It is certain that the prophets regarded God's vengeance, of which they were the heralds, with greater horror than other men; and although, in fulfilling the role assigned to them, they threatened severely, they still never set aside human feelings, so as not to have compassion on those who perished.

But the chief reason was a consideration of the covenant that God had made with the seed of Abraham; and we see that Paul also had this feeling to such an extent that he wished to be accursed for his brethren (Romans 9:3). Therefore, when Isaiah brings this fact to mind, he cannot help but be deeply affected with grief; and yet, as I have hinted, this tends to make the fact more certain, as he visualizes it as if he were actually seeing it.

The word multitude is used here because the army had been gathered from many and various nations, of which the Assyrian monarchy was composed. The metaphors he adds are intended for no other purpose than to demonstrate more forcibly what has already been stated; for he compares them to a sea or a flood, which inundates an entire country.