Job had requested a mediator from God that was made of clay, someone whose rod would not be heavy, and who would not scare him. He asked God twice for this. Elihu professes to be the man that God sent to satisfy Job's request. This is the reason God did not correct Elihu. Elihu was doing God's bidding, and was speaking with authority of God. To some Elihu seemed brash, but he was only doing God's bidding.
God states Job reproved him in Job 40:2 and is the reason that God said to Job, in Job 40:8, "Will you condemn me so that you might be righteous?" And is the reason Elihu said in Job 35:2, "Do you think it is right for you to declare yourself more righteous than God."
Elihu is only doing the bidding of God, but people have a problem with Elihu condemning Job because it doesn't fit their narrative of Job. God never said Job was righteous. God said Job was upright, and their is a big difference from being righteous, and being upright. Jesus was righteous, and the word here means without blemish. Job had many blemishes. He cursed the day he was born. He said God would laugh at the trial of the innocent, and cover the eyes of the judges. God accused Job of having a covenant with the king over the children of pride.
The bible never states the cause for God setting Satan on Job, but it should be evident to the careful reader that it was to save Job's soul. Elihu said,----
Job 33:17-25 That he may withdraw man
from his purpose, and hide pride from man. He keepeth back his soul from the pit, and his life from perishing by the sword. He is chastened also with pain upon his bed, and the multitude of his bones with strong
pain: So that his life abhorreth bread, and his soul dainty meat. His flesh is consumed away, that it cannot be seen; and his bones
that were not seen stick out. Yea, his soul draweth near unto the grave, and his life to the destroyers. If there be a messenger with him, an interpreter, one among a thousand, to shew unto man his uprightness: Then he is gracious unto him, and saith, Deliver him from going down to the pit: I have found a ransom. His flesh shall be fresher than a child's: he shall return to the days of his youth:
If those verses above are not a picture of salvation, what is?