John Calvin Commentary Isaiah 7:20

"In that day will the Lord shave with a razor that is hired in the parts beyond the River, [even] with the king of Assyria, the head and the hair of the feet; and it shall also consume the beard." — Isaiah 7:20 (ASV)

The Lord will shave with a hired razor. He now uses a different metaphor, comparing those enemies by whom the Lord had determined to afflict Judea at the appointed time to a razor, by which the beard and hair are shaved, and other such growths are removed. The Hebrew letter ב (beth) is superfluous here and is only used in accordance with Hebrew idiom to denote an instrument; therefore, I have simply rendered it he will shave with a razor. He immediately explains what he means: namely, that the Assyrians will serve as a razor in God's hand, and that they will come from a distant country.

Who are beyond the river. This means that the Euphrates will not prevent them from crossing over to execute God's commands. He also adds that it will not be some portion of that nation rushing forward on its own into foreign territories, or wandering without an established leader; rather, the king himself will lead them, so that the nation and the king together will overwhelm Judea, and it will sink under such a burden.

A hired razor. It is not without reason that he says this razor is hired, for by this he expresses the dreadful nature of the calamity that the Assyrians would bring upon them. If a man uses a hired horse or a hired sword, he will use it more freely and will not spare or take care of it as he would his own, because men wish to gain full advantage from what they have hired, to the full value of the hire.

Thus the Lord threatens that he will not spare the razor at all, even if he has to blunt it, which means he will send the Assyrians with furious violence and rage. If the Lord took such dreadful vengeance on the Jews for the reasons the Prophet previously listed, we should fear being punished in the same way; or rather, we should dread the razor with which he has already begun to shave us.

The head and the hair of the feet. By the hair of the feet he means the lower parts, for by the feet is meant all that is below the belly; this is a figure of speech where a part is taken for the whole. In short, he means that the whole body, even the beard, must be shaved.

Now, if we set aside the figures and wish to arrive at the plain and natural meaning, it is as if he said that this shaving will reach from the top of the head down to the feet. Kings and princes will not be exempt from this calamity, but they also must feel the edge of the razor.