2 - History of Pentecost – Taken from Wikipedia and edited and added to by Patrice
 
The Godly Jewish and Christian holy day of Pentecost, which is celebrated fifty (50) days after Resurrection Sunday (aka Feast of First Fruits) as God tells us exactly how to do it in Levitcus 23:15-22, commemorates the descent of the Holy Spirit upon the Apostles and other followers of Jesus Christ while they were in Jerusalem celebrating the Feast of Weeks or Shavout - aka as Pentecost, as described in the Acts of the Apostles (Acts 2:1–31).
 
In Eastern Christianity, Pentecost can also refer to the entire fifty  (50) days of Easter through Pentecost inclusive; hence the book containing the liturgical texts is called the "Pentecostarion". Since its date depends on the date of Feast of First Fruits, Pentecost is a "moveable feast". (Eastern Christianity has it right. It is not a set date decided by the evil Catholic Church and Papacy but decided exactly by God in Leviticus 23.

Pentecost is one of the Great Feasts of the Eastern Orthodox Church, a Solemnity in the Roman Rite of the Catholic Church, a Festival in the Lutheran Churches, and a Principal Feast in the Anglican Communion. Many Christian denominations provide a special liturgy for this holy celebration. And if they don't, they should!!! But most of them get it wrong because the evil Catholic Church has changed the date to be as far away from God's Feast calendar so as to confuse the masses, just as the AntiChrist likes to do.
 
The term Pentecost comes from the Greek Πεντηκοστή (Pentēkostē) meaning "fiftieth". It refers to the festival celebrated on the fiftieth day after Feast of First Fruits, also known as the "Feast of Weeks” or Shavout and the "Feast of 50 days" in rabbinic tradition.
 
The Septuagint writers used the word in two other senses: to signify the year of Jubilee (Leviticus 25:10), an event which occurs every 50th year, and in several passages of chronology as an ordinal number. The term has also been used in the literature of Hellenistic Judaism by Philo of Alexandria and Josephus. 
 
In Judaism the Festival of Weeks (Hebrew: שבועות‎ Shavuot) is a harvest festival that is celebrated seven weeks and one day after the first Sabbath - which is Feast of Firstfruits and the day Jesus rose - of the Feast of Unleavened Bread in Deuteronomy 16:9 or seven weeks and one day after the Sabbath referred to in Leviticus 23:16.
 
The Festival of Weeks is also called the Feast of Harvest in Exodus 23:16 and the day of First Fruits in Numbers 28:26, as Jews were to bring the very best of the first of their crops of the wheat harvest and barley harvest to the Lord.

In Exodus 34:22 it is called the "firstfruits of the wheat harvest." The date for the "Feast of Weeks" originally came the day after seven full weeks following the first harvest of grain. 
 
After the destruction of the Temple in 70 AD offerings could no longer be brought to the Temple and the focus of the festival shifted from agriculture to the giving of the law on Sinai. But I believe this was because the Jews and Satan wanted to distance themselves for what really happened on the Feast of Pentecost in Jerusalem in 30 AD when 3000 Jews were saved and anointed with the Holy Spirit and the Church started to spread rapidly.

Since 70 AD, it became a Jewish custom to gather at synagogue on this Feast day and read the Book of Ruth and Exodus Chapters 19 and 20. The Jews do not even realize how prophetic this is because the Book of Ruth foreshadows the Bride of Christ - the true Church!!! Exactly what the Book of Acts is all about.