Job 33:23 (ESV)

23 If there be for him an angel, a mediator, one of the thousand, to declare to man what is right for him,

In times of illness, God sends a messenger (an angel) to stand alongside the sick person and speak words of truth to him. The word mediator in this verse can be understood as interpreter. This is what Elihu wishes to be for Job: a messenger and an interpreter, who might help Job to make sense of his situation and of God’s will for his life.