Preaching from the Revised Common Lectionary during the Festival Seasons is perhaps less complicated than preaching the rest of the lectionary year. By Festival Seasons, we mean Advent/Christmas, Epiphany, Lent/Easter, Ascension Day, Pentecost Sunday, and Trinity Sunday. During those times, the lections in the Revised Common Lectionary have a unified theme suggested by the gospel reading. (See "About the Revised Common Lectionary.") The Festival Season readings were also selected with the great doctrines of the Christian faith in mind.
For example, during the Advent-Christmas cycle, themes include preparation for the Second Coming of Christ and the Incarnation. During Epiphany, the themes remind us that God is with us and God is for us. During the Lent-Easter cycle, we are reminded of the sacrificial nature of discipleship, repentance and renewal, atonement and resurrection. On the Day of Pentecost, we recall how the church has been charged and empowered to witness to the Resurrection; and on Trinity Sunday, we celebrate the triune nature of God.
As you continue to preach from the Festival Season readings, you are encouraged to look first to the gospel for the theme for the season, then to the Old Testament for hints and previews of that theme before the coming of Christ, and then finally to the epistle reading for ways that the early church either wrestled with or celebrated the teaching.