Jeremiah 17:9

What is taught here depends on what is gone before; and therefore they ought to be read together. Many lay hold on these words and mutilate them without understanding the design of the Prophet. This is very absurd: for we ought first to see what the prophets had in view, and by what necessity or cause they were led to speak, what was their condition, and then the general doctrine that may be gafilered from their words. If we wist to read the prophets with benefit, we must first consider the reason why a thing is spoken, and then elicit a general doctrine. Thus we shall be able rightly to apply this passage to a common use, if we first understand why the Prophet said, that the heart of man was insidious. He wished, no doubt, to be more earnest with the Jews; for he saw that they had so much wantonness and obstinacy, that a simple and plain doctrine would not have penetrated into their hearts. The declaration, that they are accursed who trust in men, and that no blessedness can be expected except we rely on God, ought to have been sufficient to move them; but when he saw that there was no sufficient power in such a declaration, he added, “I see how it is, the heart is wicked and vicious; so ye think that you have so much craftiness, that ye can with impunity deride God and his ministers: I, says Jehovah, I will inquire and search; for it belongs to me to examine the hearts of men.”

We hence see that there is an implied reproof, when he says, that the heart is insidious and wicked; (175) as though he had said, “Ye think yourselves in this instance wise; is not God also wise?” Isaiah says ironically the same,

“Woe to them who go down to Egypt and make secret covenants, and who trust in horses, as though they could deceive me: ye are wise, I also have a portion of wisdom.” (Isaiah 31:1)

Notice especially the expression, “Ye are wise, etc.;” that is, “Ye are not alone wise; leave to me some portions of wisdom, so that I may be wise like yourselves.” So also in this place, “Ye are deceitful and insidious, and think that I can be deceived:” for astute men are ever pleased with their own counsels, and seek to deceive God with mere trumperies. “Ye are,” he says, “very cunning; but I, Jehovah, will search both your hearts and your reins.” I cannot finish the whole to-day.

Deceitful the heart above every thing, And incurable it is,
who can know it?

The meaning is, that it is incurably deceitful; hence the question,” Who can know it?” — Ed.