John Calvin on Isaiah 17:12

12. Alas {Bogus footnote} for the multitude! Some render Woe, making it to denote execration. Sometimes, as we have seen elsewhere, it is employed in calling to a person; but on the present occasion I rather think that it betokens sorrow, {Bogus footnote} for he groans on account of the calamity which he foresees will befall Israel, and he does so either out of brotherly affection, or in order that the prophecy may make a more powerful impression on the minds of a sluggish and indolent people. It is certain, that the prophets regarded with greater horror than other men the vengeance of God, of which they were the heralds; and although, in sustaining the character assigned to them, they threatened severely, still they never laid aside human feelings, so as not to have compassion on those who perished. But the chief reason was a consideration of the covenant which 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). When therefore Isaiah brings the fact before his mind, he cannot but be deeply affected with grief; and yet, as I have hinted, it tends to make the fact more certain, when he places it before his eyes as if he actually saw it.

The word multitude is here employed, because the army had been collected out of many and various nations, of which the Assyrian monarchy was composed. The metaphors which he adds are intended for no other purpose than to exhibit more forcibly what has been already stated; for he compares them to a sea or a deluge, which overflows a whole country.