The liturgical calendar is organized around two major centers of Sacred Time: Advent, Christmas, and Epiphany; and Lent, Holy Week, and Easter, concluding at Pentecost. The rest of the year is known as Ordinary Time, from the word "ordinal," which simply means counted time (First Sunday after Pentecost, etc.).

Advent is a season of spiritual preparation for the celebration of the birth of Christ (Christmas) and looks forward to the future reign of Christ. Expectation rather than personal penitence is the central theme of the season. Advent is a preparation for rather than a celebration of Christmas. The Christmas celebration begins on Christmas Eve and continues for the next "twelve days of Christmas."

Lent is the period of the liturgical year leading up to Easter. The purpose of Lent is preparation — through prayer and penitence — for the annual commemoration during Holy Week of the Death and Resurrection of Jesus Christ, which recalls the events linked to the Passion of Christ and culminates in Easter, the celebration of the Resurrection of Jesus Christ.

Purple is normally Advent's liturgical color, associated both with the sovereignty of Christ and with penitence.

Ordinary time is always green.