Messiaen is awesome.

At the beginning of his Traiie de rythme, de couleur, et d’ornithologie,
the seven-volume treatise on which Messiaen worked from 1949
until his death, he discusses, with the support of quotations from the
work of Saint Thomas Aquinas, the difference between eternity and
time. Time is not a part of eternity, time and eternity are two absolutely
different measures of duration. Time is the measure of what is created,
eternity is God himself and is indivisible as God is indivisible. The
end of time, a vision of eternity through the suspension of musical time was Messiaen’s aim in the Quatuor pour la fin du temps, and in the works that immediately preceded it. A regular pulse draws the attention
of the listener to an awareness of. time, so the destruction of this
regularity by the addition of short time values, or, the creation of
rhythms from the addition of different durations was to provide the
contact between the listener and the eternal in order to illustrate the
theological concepts involved in Messiaen’s composition. It can be
argued that, however one organizes rhythm, it is impossible for music to
exist outside of time and that bringing about the ‘end.of musical time’
through irregular rhythms is simply an illusion. Much music, however,
depends on creating a sense of illiusion.  The listener—whether it is a
vision of a submerged cathedral in a Debussy Prelude, a primitive ritual
in Le Sacre du printemps, or simply the transporting of the listener from
the physical world to a world of some musical experience as would be the case with music with no programmatic or pictorial content. In a certain sense, the. illusion becomes the reality, if only for a short space
of time.
This is also the aim of liturgy arid liturgical music, and it is significant
that the musical traditions of the older Christian churches should
be ametrical in the sense of avoiding a sense of regular pulse, as for
example in Old Roman and Gregorian chant arid the liturgical polyphony
of the High Renaissance. It is natural that the shape of Gregorian
chant should form a constant basis of many of Messiaen’s melodies.
The use of the introit for-the-third mass of Christmas, Puer natus est
nobis, or the gradual Haec dies, from the Easter Mass in Regard de
I’Esprit de joie (no. 10 from Vingt regards sur I’Enfant-Jesus) for
instance, both freely transformed into his own modal language, are
appropriate because of the association with the Nativity in the first case
and with joy in the second, although the movement itself does not have
a specific Easter association. Many other examples occur in all periods
of his music.

Robert Sherlaw-Johnson, Rhythmic Technique and Symbolism in the Music of Olivier Messaien