Pentecost was the time when the Holy Spirit came down upon men. It is celebrated on Sunday, May 23rd in 2010, and on Sunday, May 27th in 2012.When Jesus ascended to heaven, he told his disciples:
"Do not leave Jerusalem, but wait for the gift my promised, which you have heard me speak about. For John baptized with water, but in a few days, you will be baptized with the Holy Spirit. (Acts 1:4-5)
The day of Pentecost came on the 50th day after the Sabbath of Passover week. The Holy Spirit descended from heaven when they were all in one place making a sound like "the blowing of a violent wind" (Acts 2:2). "Tongues of fire" rested on each of them (Acts 2:4). Each man began to speak in other languages as the spirit enabled them. A crowd soon gathered to see what was happening, and were amazed by what they beheld.
Peter stood up with the other disciples and spoke to the crowd, giving a sermon chronicling the resurrection of Jesus and explaining the outpouring of the Holy Spirit that the crowd was seeing. The crowd responded and Peter asked each of them to be baptized "in the name of Jesus Christ for the forgiveness of your sins." (Acts 2:38) That day, about 3,000 were added to the ranks of the believers.
The Jewish antecedents of Pentecost
"Pentecost" in Greek means "fifty". It was meant, in the tongue of the Greek speaking Jews, and thus Greek speaking Jews who were believers in Christ, to signify the Feast of Weeks, that is the Biblical feast of Shevuot. 7 weeks, that is 7x7s, were counted from the Passover and then the next day, the 50th day, the feast of Weeks was celebrated. Whereas Passover, in addition to its symbolism of redemption from Egypt, was the season of barly harvest, Shevuot was the season of wheat harvest. The counting from Passover to Shevuot was done by enumerating sheaves (omer) of barly grain, each day until the 50th day signified the end of the pre Shevuot season and the beginning of Shevuot. Thus the season in between Passover and Shevuot is known as the period of the "Counting of the Omer". Reaching back to the first century, Shevuot had other names. Because of the harvest theme, one other name was "Hag HaKatsir" - Festival of the Harvest. But a more pertinent name for the givng of the Holy Spirit event on Pentecost was "zeman matan Toratainu" - The Time of the Giving of our Torah. It was believed that Moses received the Law from God on Mt. Sinai at this time. The Law (Torah). thus, had begun from that time to became the regulatory and directive for the whole community of Israel. And at the time of this feast, the Holy Spirit, came down on the infant Church. Thus it was at this Feast and at this time that the believers in the Messiah Jesus were given not only the power for living but also their regulatory and directive from God - this time not a "Law" but the very Spirt of Jesus Himself, the Holy Spirit. This was remembered by the Church, and as non-Jewish believers in Jesus took the ascendancy over the Jewish believers, and the Law began to "drop away", the believers found that they were not left without directive and guidance as the Law had previously provided them. Jesus through His Spirit continued to do that, just as He had promised. Pentecost, thus. became an important concept and an important season for the coming generations of believers in Christ.