This is the day the Lord has made; we will rejoice and be glad in it.
Joy as a liturgical tone
During the Resurrection season and major feasts, the Church’s melodies become brighter because the content is brighter: Christ has risen, the saints rejoice, and the faithful give thanks for salvation. The melody helps the faithful pray the feast with the body and the voice.
This joy is theological. The Church is not simply changing musical style to change mood. She is confessing that Christ has conquered death, opened paradise, and filled the Church with the hope of the Resurrection.
How feast hymns teach
Feast hymns often carry triumph, thanksgiving, procession, and repeated praise. They teach the faithful what kind of day the Church is keeping. A bright Resurrection hymn says with melody what the Gospel announces with words: Christ is risen.
The contrast with Lent and Holy Week also teaches. Sober melodies form repentance and watchfulness; festal melodies form gratitude and hope. Together they let the Church receive the whole mystery of Christ with the whole person.