Mozart’s last piece was his Requiem, for which he was commissioned by a nobleman who intended to pass the piece off as his own. He never finished it, and one of his students completed the work. More recently, others have taken Mozart’s score and finished it in their own different ways.
Mozart set the Kyrie as a fugue, which is natural because of the repetitive nature of the Greek words. But this is Mozart wearing his size 15 triple-E boots, and it’s one of his very finest works in counterpoint. No composer after Mozart dared to set the Kyrie as a fugue again.
Mozart does something at the end that is astonishing. He ends with a D chord with an open fifth (D-A-D). He leaves out the F or F# which would indicate whether the chord is D Major or D minor. But tonal ambiguity is not what he is attempting here. There is no doubt that this is D minor.
That open fifth is used to illustrate space, and it is usually the space above, such as the sky. But in the last chord of the Kyrie and during the few seconds of its decay in the church, Mozart gives a glimpse of the space below, the abyss. How he does this I’ve never been able to figure out. It’s hair-raising.
Mozart: Requiem, Introit & Kyrie (Gardiner conducting English Baroque Soloists & Monteverdi Choir)