This is also known as the Feast of the Body and Blood of Christ. This feast celebrates the institution of the Eucharist at the Last Supper.
And when the hour came, he sat at table, and the apostles with him. And he said to them, “I have earnestly desired to eat this passover with you before I suffer; for I tell you I shall not eat it[b] until it is fulfilled in the kingdom of God.” And he took a cup, and when he had given thanks he said, “Take this, and divide it among yourselves; for I tell you that from now on I shall not drink of the fruit of the vine until the kingdom of God comes.” And he took bread, and when he had given thanks he broke it and gave it to them, saying, “This is my body which is given for you. Do this in remembrance of me.” (Luke 22:14-19)