“At this time the thought of death was never far from Mozart’s mind. A letter to his father says: ‘I never lie down at night without reflecting that–young as I am–I may not live to see another day. Yet no one of my acquaintances could say that in company I am morose or disgruntled.’ It is this mood that is reflected in in the C major Quintet. No music could be further removed from morose or disgruntled thoughts or feelings. But the happiness that shines through it is not the relaxed indifference of evasion: it is the result of having considered death to be ‘the best and truest friend of mankind.'”
Benjamn Britten, program note for Mozart’s C Major Quintet, K. 515 (1973)