A wicked messenger - The Septuagint: basileuv yrasuev, a bold king; instead of מלאך malach, a messenger, they had read מלך melech, a king: but they are singular in this rendering; none of the other versions have it so. He that betrays the counsels of his government, or the interests of his country, will sooner or later fall into mischief; but he that faithfully and loyally fulfils his mission, shall produce honor and safety to the commonwealth.

A wicked messenger falleth (h) into mischief: but a faithful ambassador [is] health.
(h) Brings many inconveniences both to himself and to others.

A wicked messenger falleth into mischief,.... That does not do his errand right, nor deliver his message faithfully; such an one falls from the degree of honour in which he was into disgrace; he loses his master's favour that sent him; he is degraded from his post and office: he falls "by evil", or "into evil" (r); by the evil of sin, into the evil of punishment. So wicked ministers and false teachers, such who transform themselves into the apostles of Christ and into angels of light, who corrupt the word of God, and handle it deceitfully; these shall receive their just condemnation; since they do a deal of mischief to the souls of men, and therefore shall fall into mischief themselves, even into everlasting perdition;
but a faithful ambassador is health; or, "an ambassador of truths" (s); one that performs his embassy well and truly, he is salutary, useful, and profitable to himself, and to them that send him: the word for ambassador is translated an "hinge", Proverbs 26:14; and he is so called, because upon his negotiations abroad the hinge of political affairs turn at home. An ambassador of Christ, who does his work faithfully, keeps back nothing that is profitable, but declares the whole counsel of God; the sound doctrines he delivers are health to the souls of men; as well as he is approved of God and Christ; and so it turns to his own health and advantage, who will hear one day said unto him, "Well done, good and faithful servant", Matthew 25:23.
(r) "in malum", V. L. Pagninus, Montanus, Tigurine version, Junius & Tremellius, Pisccator, &c. (s) "legatus veritatum", Montanus, Vatablus.

Those that are wicked, and false to Christ and to the souls of men, do mischief, and fall into mischief; but those that are faithful, find sound words healing to others and to themselves.

A wicked--or, "unfaithful"
messenger falleth into mischief--or, "by mischief," or "evil," and so his errand fails. Contrasted is the character of the faithful, whose faithfulness benefits others.

17 A godless messenger falls into trouble;
But a faithful messenger is a cordial.
The traditional text, which the translations also give (except Jerome, nuntius impii, and leaving out of view the lxx, which makes of Proverbs 13:17 a history of a foolhardy king and a wise messenger), has not מלאך, but מלאך; the Masora places the word along with המלאך, Genesis 48:16. And יפל is likewise testified to by all translators; they all read it as Kal, as the traditional text punctuates it; Luther alone departs from this and translates the Hiph.: "a godless messenger bringeth misfortune." Indeed, this conj. יפּל presses itself forward; and even though one read יפּל, the sense intended by virtue of the parallelism could be no other than that a godless messenger, because no blessing rests on his godlessness, stumbles into disaster, and draws him who gave the commission along with him. The connection מלאך רשׁע is like אדם רשׁע, Proverbs 11:7 (cf. the fem. of this adj., Ezekiel 3:18). Instead of בּרע is בּרעה, Proverbs 17:20; Proverbs 28:14, parallels (cf. also Proverbs 11:5) which the punctuators may have had in view in giving the preference to Kal. With מלאך, from לאך, R. לך, to make to go = to send, is interchanged ציר, from צוּר, to turn, whence to journey (cf. Arab. ṣar, to become, to be, as the vulg. "to be to Dresden = to journey" is used). The connection ציר אמוּנים (cf. the more simple ציר נאמן, Proverbs 25:13) is like Proverbs 14:15, עד אמונים; the pluralet. means faithfulness in the full extent of the idea. Regarding מרפּא, the means of healing, here to strength, refreshment, vid., Proverbs 4:22; Proverbs 12:18.

A messenger - Who is unfaithful in the execution of that which is committed to his charge. Is health - Procures benefit, as to his master, so to himself.