Solomon
Proverbs 27:17BSB·traditional attribution
As iron sharpens iron, so one man sharpens another.
Matthew Henry Presbyterian
This intimates both the pleasure and the advantage of conversation. One man is nobody; nor will poring upon a book in a corner accomplish a man as the reading and studying of men will. Wise and profitable discourse sharpens men's wits; and those that have ever so much knowledge may by conference have something added to them.
John Gill Reformed Baptist
As in water face answereth to face,.... As water is as a looking glass, in which a man may behold his own face and another's; or as the face in the water answers to the face of a man, and there is a great likeness between them.
Jamieson-Fausset-Brown Reformed
a man sharpeneth . . . friend--that is, conversation promotes intelligence, which the face exhibits.