Mass is one of the central rituals of the Catholic religion.
In the 2150s Dr. Phlox of the Enterprise NX recalled that while on Earth, he attempted to familiarize himself with several human religions, which included learning to sing chords with Tibetan high llamas and attending a Mass at Saint Peter's Square in Rome, the historic headquarters of Catholic Christianity. (ENT: "Cold Front")
In 2376 the Doctor, playing Father Mulligan in the Fair Haven holoprogram, told Tom Paris and Harry Kim that he expected the two 'sinners' in his next sunday mass. (VOY: "Fair Haven")