I recently listened to the BBC radio program on the history of the Kyrie. (See the post of 10 August.) The commentator noted that Maurice Duruflé's (1902-86) Requiem uses a lot of plainchant (going back to the roots of Western liturgical music) while embellishing the chant with all the music of the ages that has followed: Palestrina, Bach, the French impressionists, to name a few.
In this connection, I suppose Duruflé offers us a way of understanding what authentic liturgical renewal is all about: organic development. On the one hand, we should neither forget nor disdain the past; rather, we must continually refer to it as a norm for future change. On the other hand, we should be careful to avoid the error of archeologism (as Pope Pius XII called it), romanticizing the distant past and rejecting the developments of the intervening ages or whatever is new simply because it is new. To do either is to misunderstand the Church's living Tradition.
As I noted in The Reform of the Reform? A Liturgical Debate, the 20th-century liturgical movement fell (strangely enough) into both of these errors, archeologism (we might also call it antiquarianism or primitivism) and neophilism (or faddism). To oversimplify a bit for the sake of brevity, the primitivist views the liturgical, architectural and even theological developments from, say, the 4th century onward as decadent; thus everything about the early Church should be retrieved and reinstated (sackcloth and long penances excepted, of course!). The neophile, in contrast, considers only the contemporary and trendy to be relevant and pastorally suitable.
It occurred to me as I listened to the broadcast that Duruflé's nova-et-vetera approach to liturgical music is a model for authentic liturgical renewal. In a word, it's all about ressourcement, renewal through a reappropriation of the fullness of Tradition. In some respects, that happened (for example, restoring ancient collects from sacramentaries not available during the Tridentine reform). In other respects, it did not (for example, eliminating many of the priest's private prayers simply because these were medieval importations to the "pure" Roman liturgy). Considering what the schizoprenic reform actually produced, many words come to mind, one of which is Kyrie.