She says that jazz is such a great art that it cannot be taught through a book. She touches on the spiritual and healing element of jazz as an art. It does not, she says, put someone in a box. In that sense, jazz is the natural art form for an out of the box thinker. She says that other music makes one nervous but jazz calms a person. As a result, peace, ensues as a result of listening to jazz. It is, therefore, a healing art and this feature of jazz was something that she spent her life perfecting and giving herself over to. And it is this healing dimension of jazz that gives it a "spiritual" flavour.
I was not aware of her attempts to insert jazz as an art form into Catholic liturgy. This piece by Ian Corbin is a very good analysis of art in the Catholic imagination and in particular the American form of art, jazz. A Jazz Mass?
Her attempts to have jazz included in the Catholic liturgy were not realized and Corbin describes some of the potential reasons for this. Part of it relates to the problematic aspect that Catholicism has of individualism. It is precisely this kind of American individualism (recall that jazz is an American art form) that jazz seems to extol. However, this is, according to Corbin, a misunderstanding of jazz as an art form.
Briefly put, a great jazz performer like Mary Lou Williams is an exemplary specimen of the artist as heroic individual. This individualism is not of the isolating sort bemoaned by all serious observers of Americasince Tocqueville, but rather a more romantic and ultimately communal sort. Joseph Conrad, in his celebrated preface to The Nigger of the Narcissus, put forth a vision of the artist as one who descends to the "lonely region" within himself, in order to study and then speak to our capacity for delight and wonder, to the sense of mystery surrounding our lives; to our sense of pity, and beauty, and pain; to the latent feeling of fellowship with all creation—and to the subtle but invincible conviction of solidarity that knits together the loneliness of innumerable hearts: to the solidarity in dreams, in joy, in sorrow, in aspirations, in illusions, in hope, in fear, which binds men to each other, which binds together all humanity. The chief healing power of jazz, as recognized and demonstrated by Williams, is a power of precisely this sort. It emerges when an artist feels the ugliness and beauty of life and translates the feeling into melody, harmony, and rhythm. The sensitive listener hears all this and feels that she is not alone. But for all the deep fellow-feeling that jazz can inspire, it is always, at its best, individual and personal. We are moved not so much by the composition of "My Funny Valentine" as by the spontaneous, particular, irreplaceable overflow of feeling and expression that it can occasion in the performances of Miles Davis, Mary Lou Williams, or John Coltrane. The listener takes in this overflow and allows it to resonate, but it always remains irreducibly Davis's, Williams's, or Coltrane's. Jazz that lacks this personality feels stilted and contrived; it is not, in other words, great jazz