The parallelism of the two clauses is probably one of contrast. If so, the proverb is a comparison between all teaching from without and that of the light within. "The words of a man's mouth" are dark as the "deep waters" of a pool, or tank ("deep waters" being associated in the Old Testament with the thought of darkness and mystery; compare Proverbs 20:5; Psalm 69:2; Ecclesiastes 7:24); but "the wellspring of wisdom is as a flowing brook," bright and clear. The verse presents a contrast like that of Jeremiah 2:13.

The words of a man's mouth - That is, the wise sayings of a wise man are like deep waters; howsoever much you pump or draw off, you do not appear to lessen them.
The well-spring of wisdom - Where there is a sound understanding, and a deep, well-informed mind, its wisdom and its counsels are an incessant stream, מקור חכמה mekor chochmah, "the vein of wisdom," ever throwing out its healthy streams: but מקור חיים mekor chaiyim, "the vein of Lives," is the reading of eight of Kennicott's and De Rossi's MSS., and is countenanced by the Septuagint, πηγη ζωης, "the fountain of life." And so the Arabic. This is the more likely to be the true reading, because the figure of the heart propelling the blood through the great aorta, to send it to all parts of the animal system, is a favourite with Solomon, as it was with his father, David. See the note on Psalm 36:9; Proverbs 10:11, etc.

The words of a man's mouth [are as] deep (d) waters, [and] the wellspring of wisdom [as] a flowing brook.
(d) Which can never be drawn empty, but always bring profit.

The words of a man's mouth are as deep waters,.... The words of a great and mighty man; of an excellent and valuable man, as Jarchi; or of a wise man, as Aben Ezra. The doctrines which such a man has imbibed, and his heart is full of and his mouth utters, are like to "waters", pure, purifying, and refreshing; to "deep waters", which make no noise, and cannot be easily fathomed: such are the deep mysteries of grace, the wisdom of God in a mystery, spoken among them that are perfect; of which a good man makes no boast, but humbly declares; out of the abundance of his heart, his mouth speaks;
and the wellspring of wisdom as a flowing brook; there is a spring of spiritual wisdom and knowledge in him; a well of living water, springing up unto everlasting life; and from thence it flows freely and constantly; communicating itself liberally unto others, and ministering grace to the hearers, for their edification.

The well-spring of wisdom in the heart of a believer, continually supplies words of wisdom.

Wise speech is like an exhaustless stream of benefit.

4 Deep waters are the words from a man's mouth,
A bubbling brook, a fountain of wisdom.
Earlier, we added to hominis the supplement sc. sapientis, but then an unnecessary word would be used, and that which is necessary omitted. Rather it might be said that אישׁ is meant in an ideal sense; but thus meant, אישׁ, like גּבר, denotes the valiant man, but not man as he ought to be, or the man of honour; and besides, a man may be a man of honour without there being said of him what this proverb expresses. Ewald comes nearer the case when he translates, "deep waters are the heart-words of many." Heart-words - what an unbiblical expression! The lxx, which translates λόγος ἐν καρδίᾳ, has not read דברי לב, but דבר בלב (as Proverbs 20:5, עצה בלב־). But that "of many" is certainly not a right translation, yet right in so far as אישׁ (as at Proverbs 12:14) is thought of as made prominent: the proverb expresses, in accordance with the form of narrative proverbs which present an example, what occurs in actual life, and is observed. Three different things are said of the words from a man's mouth: they are deep waters, for their meaning does not lie on the surface, but can be perceived only by penetrating into the secret motives and aims of him who speaks; they are a bubbling brook, which freshly and powerfully gushes forth to him who feels this flow of words, for in this brook there never fails an always new gush of living water; it is a fountain or well of wisdom, from which wisdom flows forth, and whence wisdom is to be drawn. Hitzig supposes that the distich is antithetic; מים עמקּים, or rather מי מעמקּים, "waters of the deep," are cistern waters; on the contrary, "a welling brook is a fountain of wisdom." But עמק means deep, not deepened, and deep water is the contrast of shallow water; a cistern also may be deep (cf. Proverbs 22:14), but deep water is such as is deep, whether it be in the ocean or in a ditch. 4b also does not suggest a cistern, for thereby it would be indicated that the description, דברי פי־אישׁ, is not here continued; the "fountain of wisdom" does not form a proper parallel or an antithesis to this subject, since this much rather would require the placing in contrast of deep and shallow, of exhausted (drained out) and perennial. And: the fountain is a brook, the well a stream - who would thus express himself! We have thus neither an antithetic nor a synonymous (lxx after the phrase ἀναπηδῶν, Jerome, Venet., Luth.), but an integral distich before us; and this leads us to consider what depths of thought, what riches of contents, what power of spiritual and moral advancement, may lie in the words of a man.

A man's - A wise man's. As a brook - That wisdom which is in his heart is continually pouring forth wise and good counsels.