The word ‘tenebrae’ is Latin for shadows. The purpose of the Tenebrae service is to recreate the emotional aspects of the passion story.  At its core, the Tenebrae service works like this: It starts out with the church in candlelight. There are as many candles as there are readings, plus a white Christ candle. The readers go up one at a time, read their assigned selections, and extinguish one of the candles, until only the Christ candle remains. Then someone reads the first part of Psalm 22, which Jesus quoted on the cross. Then the Christ candle is put out, leaving the congregation in near total darkness—and near total devastation. At this point, the service ends. There is no benediction and the people leave in silence. 

The purpose of the service is to recreate the betrayal, abandonment, and agony of the events, and it is left unfinished, because the story isn’t over until Easter Day