The purpose of the church calendar is to reenact the life of Jesus Christ over the course of the year. Lectionary readings follow the theme of the season, and the holy day at the climax of the season sums up its theme.
The seasons go back to ancient times, but they were tidied up by the Consultation on Common Texts in the Revised Common Lectionary. Some churches revised their terminology. For instance, Anglicans changed the term Eastertide
to The Season of Easter.
The church year consists of two parts, the Christmas cycle, and the Easter Cycle. The Christmas cycle includes holy days whose dates are relative to Christmas, and the Easter Cycle consists of holy days whose dates are relative to Easter.
The rest of the year used to be called Ordinary Time, not because it is ordinary in the sense of bland, but because the Sundays have no traditional names, just ordinal numbers. The Consultation on Common Texts split Ordinary time into two parts. The part before the Easter cycle is called the Season After the Epiphany
and the part after the Easter cycle is called the Season After Pentecost.
The seasons are below. You can find out the beginning and ending dates of the seasons for any year you specify.
Advent
The theme of Advent consist of the events that immediately preceded Jesus’ birth.
Christmas
The theme of Christmas is the birth of Jesus Christ and the events that immediately followed.
The Season After the Epiphany
The theme of the Season After the Epipany is Jesus’ revelation of His identity to the world, beginning with the wise men at Epiphany, and ending with the disciples at the Transfiguration.
Lent
The theme of Lent is fasting, reflection, prayer, and repentance, because it reenacts the forty days that Jesus spent in the wilderness being tempted by the devil. Lent always begins on a Wednesday because it does not include the Sundays, which are always a joyous celebration of the Resurrection.
Holy Week
Holy Week may or may not be the last week of Lent, depending on your church. It begins on Palm-Passion Sunday. The theme of Holy Week is a reenactment of the events leading up to and including the crucifixion.
Easter
Easter lasts 50 days, beginning with the resurrection on Easter Day and ending with the outpouring of the Holy Spirit at Pentecost. The theme of Easter is Jesus’ triumph over death and His appearances to His disciples.
The Season After Pentecost
The Season After Pentecost lasts from Pentecost Sunday to the day before Advent, when the calendar starts over. It doesn’t have a particular theme, but it ends with prophecies of the second coming, and the last Sunday is a celebration of Jesus as King of the Universe. Under the influence of inclusive language, it is often a celebration of the kingdom rather than the King.