The Rorate Mass or (Rorate Caeli Mass) is a traditional Advent devotion in honor of the Blessed Virgin Mary. The Rorate Mass is lit only by candlelight. Because it is a votive Mass in Mary’s honor, white vestments are worn instead of Advent violet.
On a Saturday during the Advent season, the faithful gather — typically before sunrise (hence the necessity for candles) — for a special Mass.
Taken from Isaiah 45:8, which is the introit for the mass:
“Rorate, caeli, desuper, et nubes pluant justum, aperiatur terra, et germinet Salvatorem.”
“Drop down dew, ye heavens, from above, and let the clouds rain the just: let the earth be opened and bud forth a Saviour.”
From the FSSP website:
…priests and faithful prepare to honor the Light of the world, Who is soon to be born, and offer praise to God for the gift of Our Lady. As the Mass proceeds and sunrise approaches, the church becomes progressively brighter, illumined by the sun as our Faith is illumined by Christ.
The readings and prayers of the Mass foretell the prophecy of the Virgin who would bear a Son called Emmanuel, and call on all to raise the gates of their hearts and their societies to let Christ the King enter; asking for the grace to receive eternal life by the merits of the Incarnation and saving Resurrection of Our Lord.
For some stunning photos of previous Rorate Masses around the world, check this out.