Iron and Iron

Proverbs: An Introduction and Commentary Stimulating Contact (27:17)

Countenance (AV, RV) almost equals ‘personality’ here. Like ‘soul’, it can stand for the man himself (cf. RSV). See subject-study: The friend, 1 (b) 3, p. 42.

Lexham Context Commentary: Old Testament Second Collection of Assorted Proverbs of Solomon Copied by the Men of King Hezekiah (25:1–29:27)

Within this section there are two subsections, 25:2–27:27 and 28:1–29:27

The NET Bible First Edition Notes (Notes for 27:17)

Notes for 27:1738 tn The term “as” is not in the Hebrew text, but is supplied in the translation to clarify the comparison.

The NET Bible First Edition Notes Notes for 27:17

41 tn Heb “sharpens the face of his friend.” The use of the word “face” (cf. KJV, ASV “countenance”) would here emphasize that it is the personality or character that is being sharpened. Constructive criticism sharpens character. Use of the wits in interaction that makes two people sharp as a razor (W. McKane, Proverbs [OTL], 615); another example, from the Talmud, is that of two students sharpening each other in the study of the Torah (b. Ta’anit 7a).

The NET Bible First Edition-full writeup

The Book of Psalms & The Book of Proverbs Notes

This thought is resumed in 27:21 under the image of the crucible and furnace.

CSB Study Bible: Notes Chapter 27

27:17 As a file sharpens an ax or a sharpening steel a carving knife, good friends encourage one another to grow in wisdom and godliness, even if it requires painful criticism (v. 6).

It appears that the verb indicates an attempt to sharpen rather than a success (necessarily)