For Christians, Pentecost is a holiday on which we commemorate the coming of the Holy Spirit on the early followers of Jesus. Before the events of the first Pentecost, which came a few weeks after Jesus’ death and resurrection, there were followers of Jesus, but no movement that could be meaningfully called “the church.” Thus, from an historical point of view, Pentecost is the day on which the church was started. This is also true from a spiritual perspective, since the Spirit brings the church into existence and enlivens it. Thus Pentecost is the church’s birthday.
The English word “Pentecost” is a transliteration of the Greek word “pentekostos,” which means “fifty.” It comes from the ancient Christian expression “pentekoste hemera,” which means “fiftieth day,” which Christians borrowed it from Greek-speaking Jews who used the phrase to refer to a Jewish holiday. This holiday was known as the Festival of Weeks, or, more simply, Weeks (Shavuot in Hebrew). This name comes from an expression in Leviticus 23:16, which instructs people to count seven weeks or “fifty days” from the end of Passover to the beginning of the next holiday. Shavuot was the second great feast in Israel’s yearly cycle of holy days. It was originally a harvest festival (Exodus 23:16), but, in time, turned into a day to commemorate the giving of the law on Mt. Sinai. This day became especially significant for Christians because, seven weeks after the resurrection of Jesus, during the Jewish celebration of Shavuot/Pentecost, the Holy Spirit was poured out upon his first followers, gathering them together and empowering them for their mission, which was—and is—to carry out his purposes, to continue what Jesus began, to be Christ’s hand and feet in the world.