"O Lord—how long?" can just be a prayer for patience in places like the airport or the department of motor vehicles. But in Psalm 6, "O Lord—how long?" is a prayer of fear and pain: "My soul also is struck with terror, while you, O Lord—how long?" This prayer doesn't ask for the boredom, the frustration, the pain or the fear to end. It just asks: "How long?" The reassurance comes from knowing that it's not a matter of if—only when. You just have to hang on. And repeat the prayer: "O Lord—how long?"
To read more: http://www.ucc.org/daily_devotional_o_lord_how_long