Matthew Henry and continuators on Proverbs 27:2

2 Let another man praise thee, and not thine own mouth; a stranger, and not thine own lips.

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. iv. 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.