The Feast of Corpus Christi is celebrated on the Thursday after Trinity Sunday. But in virtue of the Apostolic Indult granted to the Catholic hierarchy of the United States in 1885, Masses and Processions in honor of the Most Blessed Sacrament are held on this Sunday as well, which is therefore the External Solemnity of the Feast.
It was on the cross that our Lord redeemed us, and the Holy Eucharist, instituted on the night before our Lord's Passion, remains its memorial (Collect). The altar is the extension of Calvary; the Mass "shows the death of the Lord" (Epistle). “The celebration of the Mass has the same value as the death of Jesus Christ on the Cross," St. John Chrysostom.)
We should regard the Mass as the center of all Eucharistic worship, seeing in Holy Communion the means instituted by our Lord to enable us to share more fully in this divine Sacrifice. In this way our devotion to our Lord's Body and Blood will effectively obtain for us the fruits of His Redemption (Collect). The Holy Eucharist is the pledge and the beginning of that divine life in which we shall fully rejoice in heaven (Postcommunion).
Concerning the procession which regularly should follow the Mass, we remember how the Israelites revered the Ark of the Covenant which was the Presence of God among them. When they carried on their victorious marches, the Ark went before, born by the Levites in the midst of a cloud of incense, accompanied by the sound of musical instruments and of the songs and shouts of the multitude. We Christians have a treasure far more precious, for in the Eucharist we possess God Himself. Let us feel a holy pride in forming His escort and extolling His triumphs, while He is in our midst.