In the Church's calendar there are several holy days of obligation, on which the faithful are invited to attend Mass to celebrate a specific aspect of the Catholic faith.
The feast of Corpus Christi (also known as the feast of the Body and Blood of Jesus Christ), has been for many centuries a holy day of obligation.
Initially this feast was celebrated on the Thursday after Trinity Sunday, in accord with the requests of Juliana of Liege, a 13th-century religious woman who promoted this devotion.
The purpose behind this feast was to place more emphasis on the mystery of the Holy Eucharist and how Jesus is present under the appearances of bread and wine.
St. John Paul II explains in a homily the symbolism of celebrating the feast on a Thursday.
On the Solemnity of Corpus Christi, we return to that "Thursday" which we call "Holy," on which the Redeemer celebrated his last Passover with the disciples: it was the Last Supper, fulfilling the Jewish Passover supper and inaugurating the Eucharistic rite.
For this reason, for centuries the Church has chosen Thursday for the Solemnity of Corpus Christi, feast of adoration, contemplation and exaltation. On the feast the People of God draw close to the most precious treasure left by Christ, the Sacrament of his own Presence, and they praise, celebrate and carry it in procession through the streets of our cities.
It eventually became a holy day of obligation, which meant Catholics had to stop their work week to attend Mass.
In the 20th century this became increasingly difficult in countries where there did not exist a dominant Catholic culture, and the demands of work prevented most people from attending the celebration.
As a result, the feast was moved in many places to the Sunday following Trinity Sunday to make it possible for more of the faithful to participate in the Mass of Corpus Christi.
Regardless of when it is celebrated, the feast honors the great gift of the Eucharist and how Jesus is still present in our midst.
Be sure to consult your local diocese to determine the precise date that Corpus Christi is celebrated in your area.