85. Through the sacraments of Christian initiation, the faithful become part of the Church, a prophetic, priestly and royal people called to worship God in spirit and in truth (cf. John 4, 23). The Church exercises this task through Christ in the Holy Spirit, not only in the Sacred Liturgy, especially in the celebration of the Holy Eucharist, but also in other forms of the Christian life, among which are numbered the various forms of popular piety. The Holy Spirit confers the ability to offer sacrifices of praise to God, to offer prayer and entreaty to Him, so as to make of one’s life “a living and holy sacrifice, pleasing to God” (Rm 12, 1; Heb 12, 28).
The notion of the priesthood of believers has gotten a bit battered lately. Some clergy and laity are concerned things have changed too much, or that lay people are horning in on what clergy do. But there is a deeper and more profound aspect of this role than just the considerations of ecclesiastical politics, of jealousy, or of usurpation:
86. On this priestly basis, popular piety assists the faithful in persevering in prayer and in praising God the Father, in witnessing to Christ (cf. Acts 2, 42-47), and in sustaining their vigilance until He comes again in glory. It also justifies our hope, in the Holy Spirit, of life eternal (cf. 1 Pet 3, 15) and conserves important aspects of a specific cultic context, and, in different ways and in varying degrees, expresses those ecclesial values which arise and develop within the mystical Body of Christ.
The full document, the Directory on Popular Piety and the Liturgy, is online at the Vatican site.