May 31st - Feast of the Holy Trinity

The first Sunday after Pentecost celebrates the doctrine of the three persons of God: the Father, the Son & the Holy Ghost.  Abbot Alcuin created a mass in honor of the Trinity to  combat heresy that Christ is not the Son of God in 804.  The feast was accepted and observed throughout the Catholic church in 1334.  The sign of the cross is featured prominently in the feast.