The celebration of Corpus et Sanguis Christi, Latin for the Body and Blood of Christ, is usually shortened to Corpus Christi. It began in the 13th century in Liege, Belgium in response to a vision of St. Juliana of Mont Carvillon. Pope Urban made it a feast for the whole Church in 1264. Texts for the feast are thought to have been written by St Thomas Aquinas, including a Sequence for the day, Lauda, Sion, Salvatorem or Zion, Praise your Savior.
Corpus Christi is a Holy Day of Obligation in some countries, and is celebrated on the Thursday after Trinity Sunday making a connection to the Eucharist of Holy Thursday. It was moved to Sunday in the United States in the same way that some other feasts, such as the Epiphany or the Ascension, were moved to benefit the schedules of working people.
What are we celebrating? We are honoring the presence of Christ in the Eucharist. “Real presence” might seem like an odd term. What is “unreal” presence? The word “real” means that Christ is fully present. In past times, Catholics have been ridiculed by people who thought we believe that we are eating the actual flesh and blood of Christ. We do not comprehend the reality of the Body and Blood of Christ through our senses; we believe by faith that Christ is truly present. We consume the Body and Blood of Christ, and we receive Christ in our own bodies in order to be Christ-like in the world.
A popular custom on this day is an outdoor procession. In a Corpus Christi procession, the Eucharist is solemnly carried in a monstrance along a designated route. People in the procession reverently sing and pray. They are expressing their Eucharistic devotion to the community at large. The procession honors the presence of Christ in the Eucharist in a public way.
The Church offers a number of possible ways to express our love of the Eucharist including devotional practices such as processions, Eucharistic Adoration or Exposition, and Benediction. Whether we do or don’t participate in these devotions, we need to make it clear that the reception of Communion at Mass (under both forms, it is to be hoped even in our Covid times) is the central activity in our faith.