You should not be stopped by that. Messiaen is such a complex figure that you should forget all about the religious approach. He is very sensual, in his music as in his life. His first wife went crazy or something and he married after a while a young pupil, a pianist called Yvonne Loriod; they are passionately in love, together. And this is a sin. And his music is a sin, too. It is also - also - very abstract in its scales, a very intuitive departure from the traditional scholarship into the realm of rhythmics, Indian, Greek, very pagan.” — Iannis Xenakis, a general nonprogrammicist, who was taught by Messiaen, argued that catholic mysticism is irrelevant to Messiaen’s music.
I think where Messiaen’s music loses some of its potency (Boulez writes about this) is the inclusion of “Indian” and “Greek” rhythms, because this inclusion reeks of a weak pan-spirituality and detracts from the music’s concentration on the Catholic juxtaposition of sacred/sensual. There are other criticisms of Messiaen's music but overall we're dealing with one of the 20th century's most uniquely carved souls.