Carl Friedrich Keil and Franz Delitzsch Old Testament Commentary

Four proverbs of wisdom with eloquence: 21 The wise in heart is called prudent, And grace of the lips increaseth learning. Elsewhere (Pro 1:5; Pro 9:9) הוסיף לקח means more than to gain learning, i.e., erudition in the ethico-practical sense, for sweetness of the lips (dulcedo orationis of Cicero) is, as to learning, without significance, but of so much the greater value for reaching; for grace of expression, and of exposition, particularly if it be not merely rhetorical, but, according to the saying pectus disertos facit, coming out of the heart, is full of mind, it imparts force to the instruction, and makes it acceptable. Whoever is wise of heart, i.e., of mind or spirit (לב = the N.T. νοῦς or πνεῦμα), is called, and is truly, נבון [learned, intelligent] (Fleischer compares to this the expression frequent in Isaiah, "to be named" = to be and appear to be, the Arab. du'ay lah); but there is a gift which highly increases the worth of this understanding or intelligence, for it makes it fruitful of good to others, and that is grace of the lips. On the lips (Pro 10:13) of the intelligent wisdom is found; but the form also, and the whole manner and way in which he gives expression to this wisdom, is pleasing, proceeding from a deep and tender feeling for the suitable and the beneficial, and thus he produces effects so much the more surely, and beneficently, and richly.