The Lectionary serves as the authoritative liturgical resource for the Catholic Church, organizing the scriptural readings used during the celebration of the Mass. This volume provides the structured sequence of biblical passages—drawn from the Old and New Testaments—that correspond to the liturgical calendar, including Sundays, weekdays, and feast days. It functions as the primary instrument for the proclamation of the Word of God within the communal worship of the Church, ensuring consistency in the scriptural diet of the faithful across global congregations.

The Lectionary is regarded as the essential, foundational text for Catholic liturgical practice, providing the necessary structure for the Church's public prayer life. Its authority is derived from its status as the official, approved collection of readings for the celebration of the Mass, making it a standard reference for clergy and liturgical ministers worldwide.