Pentecost

Pentecost is celebrated fifty days after Easter Sunday, and is also known as Whitsun. It commemorates the descent of the Holy Spirit upon the Apostles while they were in Jerusalem celebrating Shavout, or the Feast of Weeks, as described in the Acts of the Apostles.

Wikipedia says:-"The term Pentecost comes from the Greek Πεντηκοστή (Pentēkostē) meaning "fiftieth". It refers to the festival celebrated on the fiftieth day after Passover, also known as the "Feast of Weeks" and the "Feast of 50 days" in rabbinic tradition." Pentecost thus falls ten days after Ascension, which is forty days after Easter. 

Pentecost is regarded as the birthday of the Christian church, and the start of the church's mission to the world. The symbols associated with the festival are those of the Holy Spirit and include flames which represent the change brought about by the power of the Holy Spirit, wind which represents the breath of God and a dove to represent God's presence, as in the baptism of Jesus (Mark 1 : 10). The second chapter of the Book of Acts describes a "mighty rushing wind" (a common symbol for the Holy Spirit) and "tongues as of fire". The gathered disciples were "filled with the Holy Spirit, and began to speak in other tongues as the Spirit gave them utterance". This represents the fulfilment of the promise that Christ will baptise his followers with the Holy Spirit, mentioned in Matthew and Luke, and differentiated from John's baptism by water.

The Jewish festival of Shavout or "Feast of Weeks" is the Jewish Festival of First Fruits, or their Harvest Festival. It is prophetic therefore that the followers of Jesus should receive the gift of the Holy Spirit at this time, a time which celebrated the culmination of hard work and labour, and the gift of a reward with an eye on the future. Indeed, the verb used in Acts 2:1 to indicate the arrival of the day of Pentecost carries a connotation of fulfilment.