I have been reading as much as I can. I see where the Pentacost was prophesied by Joel and spoken of by Peter during the event. Did Jesus ever clearly refer to this event other than through the founding of the church upon Peter? And was the coming of the holy spirit foretold or expected?
Pentecost is a Greek term meaning "Fifty", used as a translation of the Jewish Feast of Shavuot. Shavuot, the Feast of Weeks, took place fifty days after Passover. Shavuot is one of the three mandatory pilgrimage feasts in Judaism, the other two being Passover and Sukkot.
In the Acts of the Apostles the text in the first chapter begins roughly where the Gospel of Luke ended (the Gospel of Luke and the Acts of the Apostles were written by the same person, traditionally believed to be St. Luke, a traveling companion of St. Paul the Apostle). Here after Jesus had been raised from the dead, but before He ascended into heaven, He instructs His disciples to remain in Jerusalem until the Holy Spirit comes.
"But you will receive power when the Holy Spirit has come upon you; and you will be my witnesses in Jerusalem, in all Judea and Samaria, and to the ends of the earth." - Acts 1:8
The Greek word apostolos (apostle) means "one that is sent out". The purpose of this book, the Acts of the Apostles, is to tell the story of how Jesus sends His apostles out into the world to be preachers of His Gospel and kingdom. This verse, Acts 1:8, is kind of like a thesis statement, the entire book follows this pattern beginning in the events in Jerusalem, then throughout Judea and Samaria, and then to the outermost reaches of the civilized (Roman) world. Indeed the text ends rather abruptly with St. Paul under house arrest in Rome.
In Acts chapter 2 Jesus' promise of the Holy Spirit coming upon His disciples comes to pass, and with this comes a courage and authority to speak they had never been shown to have previously. Upon this happening Peter stands up and preaches a lengthy sermon, and according to the text upward of about 3,000 of the pilgrims in Jerusalem were baptized as Christians.
So, yes, that the Holy Spirit was poured out on Pentecost and, thus, giving birth to the Church's call and mission toward the world is a universally held Christian belief: Roman Catholic, Eastern Orthodox, and Protestant.
-CryptoLutheran