“While they were eating, he took bread, said the blessing, broke it, gave it to them, and said, ‘Take it; this is my body.’ Then he took a cup, gave thanks, and gave it to them, and they all drank from it. He said to them, ‘This is my blood of the covenant, which will be shed for many.'”
Where the Solemnity of the Body and Blood of Christ is not observed as a holy day, it is assigned to the Sunday after Trinity Sunday, which is then considered its proper day in the calendar.
Corpus Christi (Body and Blood of Christ) is a Eucharistic solemnity, or better, the solemn commemoration of the institution of that sacrament. It is, moreover, the Church’s official act of homage and gratitude to Christ, who by instituting the Holy Eucharist gave to the Church her greatest treasure. Holy Thursday, assuredly, marks the anniversary of the institution, but the commemoration of the Lord’s passion that very night suppresses the rejoicing proper to the occasion. Today’s observance, therefore, accents the joyous aspect of Holy Thursday.
The Mass and the Office for the feast was edited or composed by St. Thomas Aquinas upon the request of Pope Urban IV in the year 1264.