John Gill's Exposition of the Whole Bible
Job 31:40
Let thistles grow instead of wheat, and cockle instead of barley,.... This is an imprecation of Job's, in which he wishes that if what he had said was not true, or if he was guilty of the crimes he denied, that when and where he sowed wheat, thorns or thistles might come up instead of it, or tares, as some Jewish writers d interpret it; and that when and where he should sow barley, cockle, or darnel, or any "stinking" or "harmful" weed e, as the word signifies, might spring up in room of it; respect seems to be had to the original curse upon the earth, and by the judgment of God is sometimes the case, that a fruitful land is turned into barrenness for the wickedness of them that dwell in it, Genesis 3:18;
the words of Job are ended; which is either said by himself, at the close of his speech; thus far says Job, and no farther, having said enough in his own defence, and for the confutation of his antagonists, and so closes in a way of triumph: or else this was added by Moses, supposed to have written this book; or by some other hand, as Ezra, upon the revision of it, and other books of the Old Testament, when put in order by him: and these were the last words of Job to his friends, and in vindication of himself; for though there is somewhat more said afterwards by him, and but little, yet to God, and by way of humiliation, acknowledging his sin, and repentance for it with shame and abhorrence; see Job 40:3. Jarchi, and so the Midrash, understand this concluding clause as all imprecation of Job's; that if he had done otherwise than he had declared, he wishes that these might be his last words, and he become dumb, and never open his mouth more; but, as Bar Tzemach observes, the simple sense is, that his words were now completed and finished, just as the prayers of David, the son of Jesse, are said to be, Psalms 72:20.
d Bar Tzemach, et alii. e באשה "herba foetens", Montanus, Bolducius; "spina foetida", Drusius; "vitium frugum", Junius Tremellius, Piscator "labrusca", Cocceius, Schultens.