Pentecost is the occasion on which the Holy Spirit descended in tongues of fire upon the Twelve Apostles. It is described in Acts 2:1-4:
And when the day of Pentecost was fully come, they were all with one accord in one place. And suddenly there came a sound from heaven as of a rushing mighty wind, and it filled all the house where they were sitting. And there appeared unto them cloven tongues like as of fire, and it sat upon each of them. And they were all filled with the Holy Ghost, and began to speak with other tongues, as the Spirit gave them utterance.
This miraculous ability to converse in previously unknown languages is called “speaking in tongues,” or xenoglossy. Today it is associated with Pentecostal and Charismatic churches and is regarded with scepticism by most mainstream faiths, but it had strong traction among the New England Puritans. Despite the narrator’s implications that speaking in tongues is a rare attribute, it was in fact considered essential for ministers.
Pentecost is celebrated seven days after Easter Sunday and is also known as Whitsun.