Because thou shalt forget thy misery, and remember it as waters that pass away:
Zophar, as the other two, here encourages Job to hope for better times if he would but come to a better temper. I. He gives him good counsel (Job 11:13, Job 11:14), as Eliphaz did (Job 5:8), and Bildad, Job 8:5. He would have him repent and return to God. Observe the steps of that return. 1.
Commenting on Job 11:13-20
Because thou shall forget thy misery,.... Former afflictions and distresses; having an abundance of prosperity and happiness, and long continued; and so, in process of time, the miseries and distresses before endured are forgotten; thus it was with Joseph in his advanced state, and therefore he called one of his sons Manasseh, Gen 41:51; and as it is with convinced and converted persons and believers...
Just as when the stream runs dry (Job 6:17), the danger threatened by its wild waves is forgotten (Isa 65:16) [UMBREIT].