Because thou shalt forget thy misery. All thy past misery shall be clean swept away from thy remembrance, because of the happy condition whereto thou shalt be raised (see Job 11:18, Job 11:19). "Sorrow's memory" is not always "a sorrow still."
And remember it as waters that pass away; i.e. remember it no more than a man remembers the shower that has passed away or the pool that is dried up.