For my people is foolish
This, as Kimchi says, is the answer of the Lord to the prophet; for not the prophet says this, but the Lord to the prophet, giving a reason why this sore destruction came upon the people of the Jews, and so reconciling his mind to the providence; seeing those whom he had chosen to be his people, above all people upon the face of the earth, and who professed themselves to be his people, had acted such a foolish part as they had done, in backsliding from him, revolting from his ways and worship, rebelling against him, and in committing such gross idolatries as they had been guilty of. So a people may be a professing people, and yet a foolish one; there are foolish professors of religion; such who take up a profession foolishly, without an experience of the grace of God; without any true faith in Christ; without having on the wedding garment of his righteousness; without laying it upon a good foundation; and without considering the cost and charge of a profession, and the difficulties and troubles attending it; and such are they who foolishly trust in it, when they have taken it up; and hold it foolishly, very remissly, and in a wavering manner; and who walk not agreeably to it, and at last foolishly drop it: they have not known me;
men may be the people of God by profession, and yet not know him; not know him so as to glorify him; not know him as their God, truly and experimentally; not know him in Christ, and have communion with him through him; not know the Lord Christ himself, the worth, glory, and excellency of him; their need of him; of his blood to cleanse them from sin; of his righteousness to justify them; of his sacrifice to atone for them; and of his fulness to supply their need; nor know the way of life, peace, and salvation by him, or at most only notionally, not experimentally; whereas the only true wisdom is to know Christ, and God in him; this is real and solid knowledge; it is science truly so called; it is delightful and satisfactory; it is useful and profitable, and is what issues in eternal life; and let men know what they will else, if they know not the Lord, they are "sottish children"; they are children indeed in understanding; and though they may be the children of God by profession, they are not the true and genuine children of God, since they know neither the Father nor the Son: and they have no understanding;
though they are not without a natural understanding, or an understanding of things natural and civil, yet they have no spiritual understanding, or an understanding of spiritual things; and at best only in a speculative, and not in an experimental way and manner: they are wise to do evil;
cunning inventors of evil things, crafty schemers that way, may be full of all wicked subtlety, and expert at over reaching and defrauding their brethren; when professors of religion especially ought to be wise unto that which is good, and simple concerning evil, ( Romans 16:19 ) : but to do good they have no knowledge;
to do good, or to do a good thing well, is to do it according to the revealed will of God, from a principle of love to him, in the exercise of faith upon him, in the name and strength of Christ, and with a view to the glory of God; to do good in this sense, and in such a way and manner, carnal men and carnal professors have no knowledge, no practical knowledge; they have no inclination to it, but the reverse; nor do they, nor can they, perform it: if they had a knowledge how to do it, or a power to perform it, there would have been, in one age or another, some, more or fewer, that would have done it; but there is none of all Adam's descendants that does good, no, not one, ( Romans 3:9-12 ) , the grace of God is absolutely necessary to the right doing of a good work, and the knowledge of it.