Gregory the Dialogist

Let the thistle grow for me instead of wheat, and the thorn instead of barley. As though he said in plain words; 'If I have done aught unjust towards those under me, if I have exacted the debts due to me, and have not myself paid what I owed, if I have envied others the executing of good practice, for the good things which refresh for ever and ever, may evil things that sting be repaid me in the Judgment.' Since 'instead of the wheat there springs up the thistle, and instead of barley the thorn,' when in the final Retribution, …

Morals on the Book of Job, Book XXII ↗

Thomas Aquinas

Now it is just that one who desires superfluous and uncommon profit loses even what is due and common. So he says, "in place of wheat," sown for the nourishment of men, "let nettles grow for me," which not only are useless, but prickly. "And for barley," which is sown as cattle feed, "the thorn," which even wounds cattle by pricking them. When he had said all these things, the epilogue comes next when it is said, "Here the words of Job end," because he proposes nothing after this to prove his proposition.

Commentary on Job ↗