Should a wise man - Referring to Job, and to his claims to be esteemed wise; see Job 12:3; Job 13:2, Job 13:6. The argument of Eliphaz here is, that the sentiments which Job had advanced were a sufficient refutation of his pretensions to wisdom. A wise man would not be guilty of "mere talk," or of using language that conveyed no ideas.
Utter - literally, answer. It refers to the replies which Job had made to the arguments of his friends.
Vain knowledge - Margin, "Knowledge of wind." So the Hebrew; see Job 6:26; Job 7:7. The "wind" is used to denote what is unsubstantial, vain, changing. Here it is used as an emblem of remarks which were vain, empty, and irrelevant.
And fill his belly - Fill his mind with unsubstantial arguments or sentiments - as little fitted for utility as the east wind is for food. The image is, "he fills himself with mere wind, and then blows it out under pretence of delivering the maxims of wisdom."
With the east wind - The east wind was not only tempestuous and vehement, but sultry, and destructive to vegetation. It passed over vast deserts, and was characterized by great dryness and heat. It is used here to denote a manner of discourse that had in it nothing profitable.

Should a wise man utter vain knowledge - Or rather, Should a wise man utter the science of wind? A science without solidity or certainty.
And fill his belly with the east wind? - בטן beten, which we translate belly, is used to signify any part of the cavity of the body, whether the region of the thorax or abdomen; here it evidently refers to the lungs, and may include the cheeks and fauces. The east wind, קדים kadim, is a very stormy wind in the Levant, or the eastern part of the Mediterranean Sea, supposed to be the same with that called by the Greeks ευροκλυδων, euroclydon, the east storm, mentioned Acts 27:14. Eliphaz, by these words, seems to intimate that Job's speech was a perfect storm or tempest of words.

Should a wise man utter (a) vain knowledge, and fill his belly (b) with the east wind?
(a) That is, vain words, and without consolation?
(b) Meaning, with matters that are of no importance, which are forgotten as soon as they are uttered, as the East wind dries up moisture as soon as it falls.

Should a wise man utter vain knowledge,.... As Job had been thought to be, or as he himself thought he was, which he might say sarcastically; or as he really was, not worldly wise, nor merely wise in things natural, but in things divine; being one that had the fear of God, which is the beginning of wisdom, and wisdom itself; believed in Christ, and walked wisely and circumspectly before men; now it is not becoming such a man to utter vain knowledge, or such knowledge as is like the wind, or, as the Targum, windy knowledge; empty, not solid, nor satisfying, but swells and puffs up, and is knowledge falsely so called; but it does not appear that Job did utter such vain and fruitless things as deserved to be compared to the wind:
and fill his belly with the east wind; which is noisy and blusterous, rapid and forcible, bearing all before it, and very infectious in hot countries; and such notions Job, according to Eliphaz, satisfied himself with, and endeavoured to insinuate them into others; which were nothing but great swelling words of vanity, and tended to subvert the faith of men, and overthrow all religion, and were very unwholesome, infectious, and ruinous to the minds of men, as suggested.

SECOND SPEECH OF ELIPHAZ. (Job 15:1-35)
a wise man--which Job claims to be.
vain knowledge--Hebrew, "windy knowledge"; literally, "of wind" (Job 8:2). In Ecclesiastes 1:14, Hebrew, "to catch wind," expresses to strive for what is vain.
east wind--stronger than the previous "wind," for in that region the east wind is the most destructive of winds (Isaiah 27:8). Thus here,--empty violence.
belly--the inward parts, the breast (Proverbs 18:8).

Fill - Satisfy his mind and conscience. East wind - With discourses not only unprofitable, but also pernicious both to himself and others; as the east - wind was in those parts.