What I find notably compelling in this composition is its regard and attention to form.
There are nine short movements: 1. Prelude 2. Exaudi 3. Dies Irae 4. Tuba mirum 5. Interlude 6. Rex tremendae 7. Lacrimosa 8. Libera me 9. Postlude. Movements 1, 5, and 9 are instrumental; the others, vocal. The structure, therefore, is 1+3+1+3+1, with the singular movements being three.
The work employs serial technique, which is beyond my knowledge to comment on. But I discern that the Catholic requiem text is abridged into canticles, that is, holy songs of praise that are not of the Psalms. So, structurally, one discerns a brief requiem arranged as nine canticles further arranged as a composite of three multiples of three, organized upon a serial tone row; thus, the integration of four levels of form. Hence, multiplicity within order.
This respect of form is further impressed upon the listener by the vocal imitation of the convention of the sounding trumpet in the Tuba mirum; the acknowledgement of the tradition of a solo alto voice in the Lacrimosa; the inspiration of rather than emulating the beatific approach of the singular soul to paradise, of the employing of chatter, as if the supplication were universal, in the Libera me; and, the sounding of welcoming bells to invoke and merge with the sounding of the call of the horn from the spiritual gates in the final ascent to what lies beyond, in the postlude.