Here are some favorite passages that answer this question.
O worship the Lord in the beauty of holiness!
In the domain of perceptible images, the artist keeps an eye constantly on the original and never allows himself to be sidetracked or to have his attention divided by any other visible object. If he does this, then one may presume to say that whatever the object he wishes to depict will, so to speak, produce a second one, so that one entity can be taken for the other, though in essence they are actually different. It is thus with those artists who love beauty in the mind. They make an image of it within their minds. The concentration and the persistence of their contemplation of this fragrant, secret beauty enables them to produce an exact likeness of God. And so these divine artists never cease to shape the power of their minds along the lines of a loveliness which is conceptual, transcendent, and fragrant, and if they practice the virtues called for by imitation of God it is not “to be seen by men,” as scripture puts it. Rather, they sacredly behold those infinitely sacred things of the Church disguised in the [rite of the] ointment, as in an image. That is why they too sacredly disguise whatever is sacred and virtuously godlike in their mind, imitating and depicting God. They gaze solely on conceptual originals. Not only do they not look at dissimilar things, but they refuse to be dragged down toward the sight of them. And as one would expect of such people, they yearn only for what is truly beautiful and right and not for empty appearances. They do not gaze after that glory so stupidly praised by the mob. Imitating God, as they do, they can tell the difference between real beauty and real evil. They are truly divine images of that infinitely divine fragrance. Because this is the truly fragrant, they have no time to return to the counterfeits which beguile the mob, and it truly impresses only those souls which are true images of itself.
—Dionysius the Areopagite
The Church, which was once the mother of poets no less than of saints, during the last two centuries has relinquished to aliens the chief glories of poetry, if the chief glories of holiness she has preserved for her own. The palm and the laurel, Dominic and Dante, sanctity and song, grew together in her soil: she has retained the palm, but forgone the laurel. And for this if song is itself responsible, we Catholics are not irresponsible. Poetry in its widest sense and when not professedly irreligious, has been too much and too long among many Catholics either misprized or distrusted; too much and too generally the feeling has been that it is at best superfluous, at worst pernicious, most often dangerous. Once poetry was, as she should be, the lesser sister and helpmate of the Church; the minister to the mind, as the Church was to the soul. But poetry sinned, poetry fell; and in place of lovingly reclaiming her, Catholicism cast her from the door to follow the feet of her pagan seducer. The separation has been ill for poetry; it has not been well for religion.
The only really effective apologia for Christianity comes down to two arguments, namely the saints the Church has produced and the art which has grown in her womb. Better witness is borne to the Lord by the splendor of holiness and art which have arisen in the community of believers than by clever excuses which apologetics has come up with to justify the dark sides which, sadly, are so frequent in the Church’s human history. If the Church is to continue to transform and humanize the world, how can she dispense with beauty in her liturgies, that beauty which is so closely linked with love and with the radiance of the Resurrection? No. Christians must not be too easily satisfied. They must make their Church into a place where beauty—and hence truth—is at home. Without this the world will become the first circle of Hell.
—Joseph Cardinal Ratzinger