Pentecost is a prominent feast in the calendar of Ancient Israel celebrating the giving of the Law on Sinai, and also later in the Christian liturgical year commemorating the descent of the Holy Spirit upon 120 disciples, including the remaining eleven apostles of Christ (Judas had hanged himself) after the Resurrection of Jesus. It is also called Whit Sunday, Whitsun, or Whit, especially in the United Kingdom, where the following Monday was traditionally a holiday. Pentecost, meaning “fiftieth day”, is celebrated seven weeks (50 days) after Easter Sunday, hence its name.
As recorded in the New Testament of the Bible, it was on the 50th day after Easter that the apostles and disciples were praying together and the Holy Spirit descended on them. They received the “gift of tongues” – the ability to speak in other languages – and immediately began to preach about Jesus Christ to Jewish people from all over the world who flocked to Jerusalem for the Feast of Shavuot.
Christian Pentecost became not only a commemoration of the Holy Spirit’s visit but also marks the birth of the Christian Church.
While not all Christians will recognize the Pentecost religious holiday as a holy day on May 15 this year, it generally is honored in liturgical churches whose congregations are Protestant, Roman Catholic, Anglican, Lutheran, Eastern Orthodox and Charismatic — and of course, Pentecostal.
Pentecost is recorded in the New Testament book known as The Acts of the Apostles. Chapter 2 begins, “And when the day of Pentecost had come, [the first followers of Jesus] were all together in one place” (2:1). All of a sudden, a sound came from heaven, like a strong wind, filling the house where the people had gathered. Something like tongues of fire rested on their heads. “And they were all filled with the Holy Spirit and began to speak in other languages as the Spirit gave them the ability to speak” (2:4).
Bible verses related to Pentecost include: Acts 2:1 — When the day of Pentecost arrived, they were all together in one place. John 14:26 — But the Helper, the Holy Spirit, whom the Father will send in my name, he will teach you all things and bring to your remembrance all that I have said to you. Titus 3:5 — He saved us, not because of works done by us in righteousness, but according to his own mercy, by the washing of regeneration and renewal of the Holy Spirit. Acts 2: 14-16 — Then Peter stood up with the Eleven, raised his voice and addressed the crowd: “Fellow Jews and all of you who live in Jerusalem, let me explain this to you; listen carefully to what I say. These people are not drunk, as you suppose. It’s only nine in the morning!” Acts 2: 42-47 — They devoted themselves to the apostles’ teaching and to fellowship, to the breaking of bread and to prayer. Everyone was filled with awe at the many wonders and signs performed by the apostles. All the believers were together and had everything in common. They sold property and possessions to give to anyone who had need. Every day they continued to meet together in the temple courts. They broke bread in their homes and ate together with glad and sincere hearts, praising God and enjoying the favor of all the people. And the Lord added to their number daily those who were being saved.
(above quoted from various internet sources)