Another form of egotism. In "understanding," i. e., self-knowledge, the "fool" finds no pleasure; but self-assertion, talking about himself and his own opinions, is his highest joy.

But that his heart may discover itself - It is a fact that most vain and foolish people are never satisfied in company, but in showing their own nonsense and emptiness. But this verse may be understood as confirming the view already given of the preceding, and may be translated thus: "But a fool doth not delight in understanding, though it should even manifest itself:" so I understand כי אם בהתגלות ki im behithgalloth. The separated person seeks understanding in every hidden thing, and feels his toil well repaid when he finds it, even after the most painful and expensive search: the other regards it not, though its secret springs should be laid open to him without toil or expense.

A fool hath no delight in understanding, but that his heart may (b) reveal itself.
(b) That is, that he may talk licentiously of whatever comes to mind.

A fool hath no delight in understanding,.... In natural understanding, and in the improvement of his mind in it; he delights not in books, nor in the conversation of men of learning and sense: or in spiritual understanding, in the understanding of spiritual things; these are foolishness to a natural man; nor does he delight in reading the Scriptures, nor in hearing the word, and attendance on it in the house of God, but is weary of such exercises;
but that his heart may discover itself; and the folly that is in it: such men only desire to have some knowledge and understanding, to make a show of it, that they may be thought to be wise, and to be capable of talking of things as if they understood them, when it is only to the exposing of themselves and their ignorance; some persons attain to no more learning and knowledge than just to be capable to show that they are fools. Or, "but in the discovery of his heart" (k); he delights in discovering that; not the wisdom, but the folly that is in it.
(k) "sed in patefacere cor ejus", Vatablus; "sed in detectione cordis sui", Piscator; "sed sane ut enudet cor suum", Schultens.

Those make nothing to purpose, of learning or religion, whose only design is to have something to make a show with.

that his heart . . . itself--that is, takes pleasure in revealing his folly (Proverbs 12:23; Proverbs 15:2).

2 The fool hath no delight in understanding;
But only that his heart may reveal itself therein.
The verb חפץ forms the fut. יחפּץ as well as יחפּץ; first the latter from חפץ, with the primary meaning, to bow, to bend down; then both forms as intransitive, to bend oneself to something, to be inclined to something, Arab. 'ṭf. (Fl.). תּבוּנה is here the intelligence which consists in the understanding of one's own deficiency, and of that which is necessary to meet it. The inclination of the fool goes not out after such intelligence, but (כּי אם־; according to Ben-Naphtali, כי־אם) only that his heart, i.e., the understanding which he thinks that he already possesses, may reveal itself, show itself publicly. He thinks thereby to show himself in his true greatness, and to render a weighty service to the world. This loquacity of the fool, proceeding from self-satisfaction, without self-knowledge, has already, Proverbs 12:23, and often, been reprimanded.

Understanding - In getting sound and saving, knowledge. The discovery - In uttering that folly and wickedness which is in his heart.