On the Vatican site, the DPPL doesn’t single out section 29 as the discussion turns to the Middle Ages. Let’s take all five paragraphs today and offer a few brief comments on them.
28. Among the main concerns of the Oriental Christian Churches, especially the Byzantine Church, of the middle ages, mention can be made of both phases of the struggles against the iconoclast heresy (725-787 and 815-843) which was a watershed for the Liturgy. It was also a period of classical commentaries on the Eucharistic Liturgy and on the iconography for buildings set aside for worship.
Those classical commentaries began with the four Eastern Doctors, and included significant writings on Christian initiation as well.
In the liturgical field, there was a noticeable increase in the Church’s iconographical patrimony and in her sacred rites which assumed a definitive form. The Liturgy reflected the symbolic vision of the universe and a sacral hierarchical vision of the world. In this vision, we have the coalescence of all orders of Christian society, the ideals and structures of monasticism, popular aspirations, the intuitions of the mystics and the precepts of the ascetics.
In addition to the previously mentioned St Gregory the Great, Saint Benedict of Nursia probably contributed much through his monastic Rule to the environment for good liturgy and spiritual/religious devotion.
Later advances in knowledge and the way we observe the universe in no way denigrate the best of the medieval traditions. Doubtless, the centuries between the fall of Rome and the Reformation saw much good seed sown and much good fruit that forms a firm foundation for Christianity to this day.
More on the icon:
With the decree De sacris imaginibus of the Second Council of Nicea (787)(In DS 600-603) and the resolution of the iconoclastic controversy in the “Triumph of Orthodoxy” (843), iconography, having been given doctrinal legitimacy, developed and organized its definitive form. The icon, hieratic and pregnant with symbolic power, itself became part of the celebration of the Liturgy, reflecting, as it did, the mystery celebrated and retaining something of its permanent presence which was exposed for the veneration of the faithful.
Moving to the Christian West:
In the West, the high middle ages saw the formation of new cultures, and political and civil institution deriving from the encounter of Christianity, already by the fifth century, with peoples such as the Celts, the Visigoths, the Anglo Saxons, and the Franco-Germans.
Would you agree with this assessment of dualism:
Between the seventh and the fifteenth century, a decisive differentiation between Liturgy and popular piety began to emerge which gradually became more pronounced, ending eventually in a dualism of celebration. Parallel with the Liturgy, celebrated in Latin, a communitarian popular piety celebrated in the vernacular emerged.
Were these two tracks more harmful to Christianity? Aside from the undeniable fruits of both the Latin liturgy and vernacular piety, did these parallel vectors create more work, more confusion, more fragmentation of the Church? Does the modern liturgy go too far in the direction of vernacular piety in losing Latin? Or was it long overdue, perhaps by a millennium or more? Consider that Orthodox Christianity maintains various sacral languages, and do their traditions inform Roman Catholics in any way with regard to liturgy and piety?
The full document, the Directory on Popular Piety and the Liturgy, is online at the Vatican site.