Gird up thy loins - See Job 38:1-3. Some think that this and the preceding verse have been repeated here from Job 38:1-3, and that several of the words there, here, and Job 42:3, have been repeated, in after times, to connect some false gatherings of the sheets of parchment, on which the end of this poem was originally written. See on Job 40:1; (note), and at the end of the chapter.
Gird up thy loins now like a man - An expression taken from the ancient mode of dress. That was a loose, flowing robe, which was secured by a girdle when traveling, or when one entered upon anything requiring energy; see the notes at Matthew 5:38-41. The meaning here is, “Prepare thyself for the highest effort that can be made. Put forth all your strength, and explain to me what will now be said;” compare the notes at Isaiah 41:21.
I will demand of thee - Hebrew “I will ask of thee.” That is, I will submit some questions to you to be answered.
And declare thou unto me - Hebrew “Cause me to know.” That is, furnish a satisfactory answer to these inquiries, so as to show that you understand the subject. The object is to appeal to the proofs of divine wisdom, and to show that the whole subject was far above human comprehension.