Gird up now thy loins like a man - To gird up the loins, is a phrase which has allusion to the mode of dress in ancient times. The loose flowing robe which was commonly worn, was fastened with a girdle when men ran, or labored, or engaged in conflict; see the notes at Matthew 5:38-41. The idea here is, "Make thyself as strong and vigorous as possible; be prepared to put forth the highest effort." God was about to put him to a task which would require all his ability - that of explaining the facts which were constantly occurring in the universe. The whole passage is ironical. Job had undertaken to tell what he knew of the divine administration, and God now calls upon him to show his claims to the office of such an expositor. So wise a man as he was, who could pronounce on the hidden counsels of the Most High with so much confidence, could assuredly explain those things which pertained to the visible creation. The phrase "like a man" means boldly, courageously; compare the notes at 1-Corinthians 16:13.
I will demand of thee, and answer thou me - Margin, as in Hebrew, "make me known." The meaning is, "I will submit some questions or subjects of inquiry to you for solution. Since you have spoken with so much confidence of my government, I will propose some inquiries as a test of your knowledge."

Gird up now thy loins - I will not confound thee with my terrors; dismiss all fearful apprehensions from thy mind; now act like a man, כגבר kegeber, like a hero: stand and vindicate thyself. For I will demand of thee - I will ask thee a series of questions more easy of solution than those which thou hast affected to discuss already; and then thou shalt have the opportunity of answering for thyself. The most impressive and convincing manner of arguing is allowed to be that by interrogation, which the Almighty here adopts. The best orations delivered by the ancients were formed after this manner. That celebrated oration of Cicero against Catiline, which is allowed to be his masterpiece, begins with a multitude of short questions, closely pressed upon each other. See the end of the chapter, Job 38:40 (note).

Gird up now thy loins like a man; for I (c) will demand of thee, and answer thou me.
(c) Because he wished to dispute with God, (Job 23:3), God reasons with him, to declare his rashness.

Gird up now thy loins like a man,.... Like a man of valour that girds on his harness for battle: Job is bid to prepare for the controversy the Lord was entering into with him; and bring forth his strong reasons and most powerful arguments in his own defence. The allusion is to the custom in the eastern countries, where they wore long garments, to gird them about their loins, when they engaged in work or war. Job had blustered what he would do, and now he is dared to it; see Job 23:4;
for I will demand of thee, and answer thou me; put questions to him, to which he required a direct and positive answer. Jehovah takes the part of the opponent in this dispute, and gives that of the respondent to Job; since Job himself had put it to his option which to take, Job 13:22.

a man--hero, ready for battle (1-Corinthians 16:13), as he had wished (Job 9:35; Job 13:22; Job 31:37). The robe, usually worn flowing, was girt up by a girdle when men ran, labored, or fought (1-Peter 1:13).

Gird up - As warriors then did for the battle.