| Barnes' Notes on the Bible Another - An "alienus" rather than "alius." Praise to be worth anything must be altogether independent.
Clarke's Commentary on the BibleLet another man praise thee, and not thine own mouth - We have a similar proverb, which illustrates this: "Self-praise is no commendation."
Gill's Exposition of the Entire BibleLet another man praise thee, and not thine own mouth,.... Men should do those things which are praiseworthy; and should do them openly, that they may be seen and praised for them: for it is honourable to have such a character as Demetrius had, who had a good report of all men; and as the brother had, whose praise in the Gospel was in all the churches. To be commended by others, by any but a man's self, is to his credit and reputation; but nothing more hurtful to it than self-commendation; see 2 Corinthians 10:18; in some cases it is right for a man indeed to commend himself, when the glory of God, the credit of religion, the cause of truth and self-vindication, require it; as the prophet Samuel, the Apostle Paul, and others, have been obliged to do, 1 Samuel 12:3, &c. a stranger, and not thine own lips; a stranger means any other than a man's self; and if it is one that he knows not, or has little acquaintance with; or if a foreigner, that does not personally know him, only has good testimonies of him, or has read his works; and especially if in other respects an enemy; it is greatly to his honour to be praised by him: and such a commendation comes with much better grace than from himself, and from whom indeed it would not come with any.
Keil and Delitzsch Biblical Commentary on the Old Testament2 Let another praise thee, and not thine own mouth; A stranger, and not thine own lips. The negative לא is with פיך, as in (Arab.) ghyra fyk, bound into one compact idea: that which is not thine own mouth (Fleischer), "not thine own lips," on the other hand, is not to be interpreted as corresponding to it, like אל־מות, Proverbs 12:28; since after the prohibitive אל, יהללוּך [praise thee] easily supplies itself. זר is properly the stranger, as having come from a distance, and נכרי he who comes from an unknown country, and is himself unknown (vid., under Proverbs 26:24); the idea of both words, however, passes from advena and alienigena to alius. There is certainly in rare cases a praising of oneself, which is authorized because it is demanded (2 Corinthians 11:18), which, because it is offered strongly against one's will, will be measured by truth (Proverbs 10:13); but in general it is improper to applaud oneself, because it is a vain looking at oneself in a glass; it is indecent, because it places others in the shade; imprudent, because it is of no use to us, but only injures, for propria laus sordet, and as Stobus says, οὐδὲν οὕτως ἄκουσμα φορτικὸν ὡς καθ ̓ αὑτοῦ ἔταινος. Compare the German proverb, "Eigenlob stinkt, Freundes Lob hinkt, fremdes Lob klingt" [ equals self-praise stinks, a friend's praise is lame, a stranger's praise sounds].
Geneva Study BibleLet another man praise thee, and not thine own mouth; a stranger, and not thine own lips.
Jamieson-Fausset-Brown Bible Commentary2. Avoid self-praise.
Matthew Henry's Concise Commentary27:1 We know not what a day may bring forth. This does not forbid preparing for to-morrow, but presuming upon to-morrow. We must not put off the great work of conversion, that one thing needful. 2. There may be occasion for us to justify ourselves, but not to praise ourselves. 3,4. Those who have no command of their passions, sink under the load. 5,6. Plain and faithful rebukes are better, not only than secret hatred, but than love which compliments in sin, to the hurt of the soul. 7. The poor have a better relish of their enjoyments, and are often more thankful for them, than the rich. In like manner the proud and self-sufficient disdain the gospel; but those who hunger and thirst after righteousness, find comfort from the meanest book or sermon that testifies of Christ Jesus. 8. Every man has his proper place in society, where he may be safe and comfortable.
Matthew Henry's Whole Bible CommentaryVerse 2 Note, 1. We must do that which is commendable, for which even strangers may praise us. Our light must shine before men, and we must do good works that may be seen, though we must not do them on purpose that they may be seen. Let our own works be such as will praise us, even in the gates, Phil. 4:8. 2. When we have done it we must not commend ourselves, for that is an evidence of pride, folly, and self-love, and a great lessening to a man's reputation. Every one will be forward to run him down that cries himself up. There may be a just occasion for us to vindicate ourselves, but it does not become us to applaud ourselves. Proprio laus sordet in ore-Self-praise defiles the mouth. | 
