From J.B. O'Connell, Church Building and Furnishing: The Church's Way. University of Notre Dame Press, 1955, pp. 39-40:

The Church does not reject what is modern in art [...] and gives great freedom to the artist who undertakes a work of sacred art, but she does emphatically reject degraded art (which for convenience sake we term here "modernistic art," using "modern" for good contemporary art). This art--which is over subjective, often bizarre and extravagant, sometimes coarse or even barbaric, the product of undisciplined sentimentalism and mere ephemeral whim, idiosyncratic--desires to pass off as beautiful the deformed and the grotesque and "loses itself in the wild forest of cubist and abstract art." [fn: Cardinal Constantini, Osservatore Romano, July 23, 1942.] This errant art arises from false ideas about originality, modernity and progress. True modernity, based on the honest desire to make the arts more effective in the service of religion makes use of diversity of style and fashion without becoming its slave, employs the living art and living creative intelligence of our own day as the great artists of the past used the art and intelligence of their day. [...]

Pius XI in his discourse at the opening of the new Vatican Art Gallery (October 28, 1932) spoke of "so many works of art indisputably and forever beautiful...which bring to mind, by an irresistible force of contrast, certain other so-called works of art, that seem to recall the sacred, only to distort it to the point of caritcature, very often of real profanation. An attempt to defend this is made on the plea of the search for the new [...]. The new represents no new progress if it is not at least as beautiful and as good as the old." The same enlightened Pontiff declared: "The so-called modern art in religion must not disfigure the House of God. Sacred art has no foundation or reason for its existence unless it represents spiritual ideals. Works of art that are foreign to the Christian tradition must not be admitted into places of prayer."