Pope Pius defends liturgy as important, sacred and sacramental. Liturgy is more than the sum of liturgical actions and prescriptions. It is an error, consequently, and a mistake to think of the sacred liturgy as merely the outward or visible part of divine worship or as an ornamental ceremonial. No less erroneous is the notion that it consists solely in a list of laws and prescriptions according to which the ecclesiastical hierarchy orders the sacred rites to be performed. The encyclical has four parts.