Ghost Story : Der Schildwache Nachtlied

Another ghost story from the Des Knaben Wunderhorn collection of Brentano and Arnim in the version adapted by Mahler for his song Der Schildwache Nachtlied.  The sentry is determined to do his duty because so many depend on his vigilance.  But he hears a mysterious voice :
 "Ich kann und mag nicht fröhlich sein;
Wenn alle Leute schlafen,
So muß ich wachen,
Muß traurig sein."

"Ach Knabe, du sollst nicht traurig sein,
Will deiner warten,
Im Rosengarten,
Im grünen Klee."

"Zum grünen Klee, da komm ich nicht,
zum Waffengarten
Voll Helleparten
Bin ich gestellt."

"Stehst du im Feld, so helf dir Gott,
An Gottes Segen
Ist alles gelegen,
Wer's glauben tut."

"Wer's glauben tut, ist weit davon,
Er ist ein König,
Er ist ein Kaiser,
Er führt den Krieg."

What's happening ? The sentry's doing his job even though he's not too happy about it. So what is this voice he's hearing ?  Is it a ghost, a memory or his subconscious? He's stuck in the "Garden of Weapons" and must deny the "Rose Garden" and the meadow of green clover, which might symbolize home, or freedom. The voice reminds him, though, that the Kaiser isn't all-powerful.  In the battlefield, anything can happen : only God decides.  But the sentry tries to blank out alternatives. Three times he repeats what controls him : King, Emperor, war.  Notice how Mahler uses major and minor to contrastb the voices, underlining the "military" with drumbeats and horns.But suddenly, something happens. Is the sentry confronted by an enemy ?  Or is the voice an expression of his subconcious longing for freedom ?  
Halt! Wer da? Rund! Bleib' mir vom Leib! 

Then a brief interlude.

"Wer sang es hier? Wer sang zur Stund'?
Verlorne Feldwacht
Sang es um Mitternacht.
Mitternacht! Feldwacht!"

Whatever has happened, the sentry is no longer among the living. He's gone.  As so often in Mahler, being dead isn't the end. What's left of the sentry is his ghostly song, echoing his worldly orders "Midnight ! Sentry! "