Today is Corpus Christi Sunday. You may wonder why Corpus Christi begins with Thursday in the first place. It is on account of the fact that it was on a Thursday that the Blessed Sacrament of the Eucharist, the Sacrificial Rite of the Mass and the Sacred Priesthood were all instituted at the Last Supper.
In memory of that first Holy Thursday we now celebrate all these wonderful things. Since Holy Thursday was too close to the sufferings of Our Lord to offer any but the briefest celebration of such a momentous gift as the Eucharist, the Church took the first suitable opportunity after Holy Week and Eastertide were over, to return at greater leisure to celebrate this gift.
So it came about that on the same weekday, namely the Thursday following Trinity Sunday, after the white days of Paschal - or Eastertide are over and we have returned to “Ordinary Time” with its green vestments, the Church established the tradition of this joyful celebration of our Lord’s Body and Blood in the Blessed Sacrament. ~ FR. PAUL DOBSON