The proverb expresses the gain of mutual counsel as found in clear, well-defined thoughts. Two minds, thus acting on each other, become more acute. This is better than to see in "sharpening" the idea of provoking, and the point of the maxim in the fact that the quarrels of those who have been friends are bitter in proportion to their previous intimacy.

Iron sharpeneth iron - As hard iron, viz., steel, will bring a knife to a better edge when it is properly whetted against it: so one friend may be the means of exciting another to reflect, dive deeply into, and illustrate a subject, without which whetting or excitement, this had never taken place. Had Horace seen this proverb in the Septuagint translation when he wrote to the Pisos?
Ergo fungar vice cotis, acutum
Reddere quae ferrum valet, exors ipsa secandi.
Hor. Ars. Poet., ver. 304.
"But let me sharpen others, as the hone
Gives edge to razors, though itself have none."
Francis.

Iron sharpeneth iron; so a (g) man sharpeneth the countenance of his friend.
(g) One hasty man provokes another to anger.

Iron sharpeneth iron,.... A sword or knife made of iron is sharpened by it; so butchers sharpen their knives;
so a man sharpeneth the countenance of his friend; by conversation with him; thus learned men sharpen one another's minds, and excite each other to learned studies; Christians sharpen one another's graces, or stir up each other to the exercise of them, and the gifts which are bestowed on them, and to love and to good works. So Jarchi and Gersom understand it of the sharpening of men's minds to the learning of doctrine; but Aben Ezra, takes it in an ill sense, that as iron strikes iron and sharpens it, so a wrathful man irritates and provokes wrath in another. Some render the words, "as iron delighteth in iron, so a man rejoiceth the countenance of his friend", (i): by his company and conversation.
(i) "laetatur", a "laetari; ferrum in ferro laetatur, et virum laetificant ora socii ejus", Gussetius, p. 242. "ferrum ferro hiluratur, et vir exhilarat vultum sodalis sui", Schultens.

We are cautioned to take heed whom we converse with. And directed to have in view, in conversation, to make one another wiser and better.

a man sharpeneth . . . friend--that is, conversation promotes intelligence, which the face exhibits.

This proverb expresses the influence arising from the intercourse of man with man:
Iron is sharpened by iron,
And a man may sharpen the appearance of another.
When the Masora reads יחד, Ewald remarks, it interprets the word as denoting "at the same time," and the further meaning of the proverb must then accord therewith. Accordingly he translates: "iron together with iron! and one together with the face of another!" But then the prep. ב or עם is wanting after the second יחד - for יחד is, in spite of Ewald, 217h, never a prep. - and the "face," 17b, would be a perplexing superfluity. Hitzig already replies, but without doing homage to the traditional text-punctuation, that such a violence to the use of language, and such a darkening of the thought, is not at all to be accepted. He suggests four ways of interpreting יחד: (1) the adverb יחד, united, properly (taken accusat.) union; (2) יחד, Psalm 86:11, imper. of the Piel יחד, unite; (3) יחדּ, Job 3:6, jussive of the Kal חדה, gaudeat; and (4) as Kimchi, in Michlol 126a, jussive of the Kal חדה (= חדד) acuere, after the form תחז, Micah 4:11. ויּחץ, Genesis 32:8, etc. in p. יחד, after the form אחז, Job 23:9. ויּחל, 2-Kings 1:2 (= ויּחלא, 2-Chronicles 16:12). If we take יחד with בּרזל, then it is priori to be supposed that in יחד the idea of sharpening lies; in the Arab. iron is simply called hadyda = חדוּד, that which is sharpened, sharp; and a current Arab. proverb says: alḥadyd balḥadyd yuflah = ferrum ferro diffinditur (vid., Freytag under the word falah). But is the traditional text-punctuation thus understood to be rightly maintained? It may be easily changed in conformity with the meaning, but not so that with Bttcher we read יחד and יחד, the fut. Kal of חדד: "iron sharpeneth itself on iron, and a man sharpeneth himself over against his neighbour" - for פני after a verb to be understood actively, has to be regarded as the object - but since יחד is changed into יחד (fut. Hiph. of חדד), and יחד into יחד or יחד (fut. Hiph. of חדד, after the form אחל, incipiam, Deuteronomy 2:25, or אחל, profanabo, Ezekiel 39:7; Numbers 30:3). The passive rendering of the idea 17a and the active of 17b thus more distinctly appear, and the unsuitable jussive forms are set aside: ferrum ferro exacuitur, et homo exacuit faciem amici sui (Jerome, Targ., the Venet.). But that is not necessary. As ויּעל may be the fut. of the Hiph. (he brought up) as well as of the Kal (he went up), so יחד may be regarded as fut. Kal, and יחד as fut. Hiph. Fleischer prefers to render יחד also as Hiph.: aciem exhibet, like יעשׁיר, divitias acquirit, and the like; but the jussive is not favourable to this supposition of an intransitive (inwardly transitive) Hiph. It may indeed be said that the two jussives appear to be used, according to poetic licence, with the force of indicatives (cf. under Proverbs 12:26), but the repetition opposes it. Thus we explain: iron is sharpened [gewetzt, Luther uses this appropriate word] by iron (ב of the means, not of the object, which was rather to be expected in 17b after Proverbs 20:30), and a man whets פני, the appearance, the deportment, the nature, and manner of the conduct of his neighbour. The proverb requires that the intercourse of man with man operate in the way of sharpening the manner and forming the habits and character; that one help another to culture and polish of manner, rub off his ruggedness, round his corners, as one has to make use of iron when he sharpens iron and seeks to make it bright. The jussive form is the oratorical form of the expression of that which is done, but also of that which is to be done.

Iron - Iron tools are made sharp and fit for use, by rubbing them against the file, or some other iron. The countenance - The company or conversation of his friend.