Also known as the Feast of Corpus Christi. For Catholics, every Sunday is a feast of the Eucharist. Nonetheless, over the centuries, a desire to specifically celebrate the Eucharist developed. The feast of Corpus Christi owes a rather large debt to St. Juliana, a nun of Liege, Belgium, who was led to start a celebration of the Mass around AD 1230. (excerpt from http://www.churchyear.net/corpuschristi.html)
The Eucharist is “the source and summit of the Christian life.” “The other sacraments, and indeed all ecclesiastical ministries and works of the apostolate, are bound up with the Eucharist and are oriented toward it. For in the blessed Eucharist is contained the whole spiritual good of the Church, namely Christ himself, our Pasch” (CCC 1324).