Pentecost is the Greek name for Shavuot, the Feast of Weeks, a prominent feast in the calendar of ancient Israel celebrating the giving of the Law to Moses at Sinai. In Christianity, Pentecost is celebrated fifty days after Easter Day, counting inclusively (including both the first and last days), i.e. seven weeks after Easter Day. In Judaism, Shavuot is on the sixth day of the Hebrew month of Sivan (late May or early June). Pentecost falls on the tenth day after Ascension Thursday (which itself is 40 days after Easter).
The feast is also called White Sunday, or "Whitsunday", especially in the United Kingdom, where traditionally the next day, Whit Monday, was also a public holiday. In Eastern Christianity, Pentecost can also refer to the entire fifty days between Easter and Pentecost, hence the book containing the liturgical texts for Paschaltide is called the Pentecostarion.
Pentecost is the old Greek and Latin name for the Jewish Festival of Weeks which can be found in the Hebrew Bible. It is called by that name in Exodus 34:22 and Deuteronomy 16:10. It is also called the Festival of Reaping in Exodus 23:16, and Day of the First Fruits in Numbers 28:26.
Jews traditionally read the Book of Ruth at Pentecost, as the story links with the grain harvest theme of the festival.
In the New Testament, Pentecost was the occasion of the descent of the Holy Spirit upon the Apostles and other followers of Jesus Christ, as described in the Acts of the Apostles 2:1–31. Thus in the Christian liturgical year it became a feast commemorating this occasion. For this reason, Pentecost is described by some Christians as the "Birthday of the Church". The Pentecostal movement of Christianity derives its name from this New Testament event, as the movement emphasizes direct personal experience with God, akin to the Descent of the Holy Spirit upon the Apostles.
The biblical narrative of Pentecost is given in the second chapter of the Book of Acts. Present were about one hundred and twenty followers of Christ (Acts 1:15), including the Twelve Apostles (i.e. the Eleven faithful disciples and Matthias who was Judas' replacement) (Acts 1:13, 26), his mother Mary, various other women disciples and his brothers (Acts 1:14).
Their reception of the Holy Spirit in the Upper Room is recounted in Acts 2:1–6:
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 Spirit, and began to speak with other languages, as the Spirit gave them utterance. And there were dwelling at Jerusalem Jews, devout men, out of every nation under heaven. Now when this was noised abroad, the multitude came together, and were confounded, because that every man heard them speak in his own language.
While those on whom the Spirit had descended were speaking in many languages, the Apostle Peter stood up with the eleven and proclaimed to the crowd that this event was the fulfillment of the prophecy ("I will pour out my spirit"). In Acts 2:17, it reads: "'And in the last days,' God says, 'I will pour out my spirit upon every sort of flesh, and your sons and your daughters will prophesy and your young men will see visions and your old men will dream dreams." He also mentions (2:15) that it was the third hour of the day (about 9:00 am). Acts 2:41 then reports: "Then they that gladly received his word were baptized: and the same day there were added unto them about three thousand souls."
Peter stated that this event was the beginning of a continual outpouring that would be available to all believers from that point on, Jews and Gentiles alike.
