O ye simple - פתאים pethaim, ye that are deceived, and with flattering words and fair speeches deluded and drawn away.
Ye fools - כסילים kesilim, ye stupid, stiffnecked, senseless people. That preaching is never likely to do much good, that is not pointed; specifying and describing vices, and charging them home on the consciences of transgressors. Where this is not done, the congregation is unconcerned; no man supposes he has any thing to do in the business, especially if the preacher takes care to tell them, "These were the crimes of Jews, Romans, Greeks, of the people at Corinth, Philippi, Thessalonica, Laodicea, and of heathens in general; but I hope better things of you, who have been born in a Christian land, and baptized in the Christian faith." Thus he arms their consciences in double brass against the good effects of his own teaching.

O ye simple, understand wisdom,.... The Gospel, the wisdom of God in a mystery, particularly the doctrine of salvation by Christ; it is the highest wisdom to know Christ and him crucified: and they are "the simple" who are weak and easy to be imposed upon, who are here called unto; and generally speaking such are they to whom the mysteries of grace are made known, while they are hid from the wise and prudent;
and ye fools, be of an understanding heart; or "cause the heart to understand"; or "get an understanding heart" (t); make use of all means to get spiritual wisdom and understanding; all men, let them be what they will in other respects, are fools as to a spiritual and experimental knowledge of divine things; and that man can only be said to have truly an understanding heart that knows his own folly, the plague of his heart, his need of Christ, the worth of him; and has an understanding given him to know him and his interest in him.
(t) "facite cor intelligere", Baynus, Mercerus; "facite ut cor vestrum intelligat", so some in Vatablus; "acquirite animum sapientem", Gejerus.

wisdom--literally, "subtilty" in a good sense, or, "prudence."
fools--as Proverbs 1:22.

Regarding ארמה, calliditas, in a good sense, vid., at Proverbs 1:4; regarding פּתאים, those who are easily susceptible of good or bad, according to the influence that is brought to bear upon them, vid., also Proverbs 1:4; and regarding כּסילים, the intellectually heavy, dull persons in whom the flesh burdens the mind, vid., at Proverbs 1:22. לב is parallel with ערמה, for the heart (according to its Semitic etymon, that which remains fast, like a kernel, the central-point) is used for the understanding of which it is the seat (Psychol. p. 249), or heartedness = intelligence (cf. חסר־לב, Proverbs 6:32 = ἄνους or ἄλογος). We take ערמה and לב as objective, as we have translated: that which is in both, and in which they consist. Thus הבּין, which is a favourite word with this author, has both times the simple transitive meaning of the gain of understanding into the nature and worth of both; and we neither need to interpret the second הבינוּ in the double transitive meaning, "to bring to understanding," nor, with Hitzig, to change in into הכינוּ
(Note: Vid., the Hebr. Zeitschrift, החלוץ, 1856, p. 112.) direct, i.e., applicate.

Ye simple - Who want knowledge, and experience. Fools - Wilful sinners.