This Sunday is the 50th day after Easter, the day of Pentecost. This, along with Easter and Christmas, is one of the 3 chief festivals of the Christian Year. On Pentecost we commemorate the outpouring of the Holy Spirit upon the disciples, for the preaching of the Gospel to the ends of the earth.
O send forth thy Spirit, and they shall be made:
and thou shalt renew the face of the earth (Psalm 104).
Come, Holy Ghost, fill the hearts of thy faithful people:
and kindle in them the fire of thy love.
Read a reflection upon the Collect for Pentecost here.