Matthew Poole and continuators on Proverbs 27:17

17 Iron sharpeneth iron , so a man sharpeneth the countenance of his friend .

Iron cutting tools are made bright, and sharp, and fit for use by rubbing them against the file, or some other Iron.

So a man, who being alone is sad, and dull, and unactive, by the company and conversation of his friend, is greatly refreshed, his very wits are sharpened, and his spirit revived, and he is both fitted for and provoked to action. The countenance is here put for the mind or spirit, whose temper or disposition is commonly visible in mens countenances.