If you go back and read the Old Testament, you will discover that Pentecost was one of the Jewish feast days. Only they didn't call it Pentecost. That's the Greek name. The Jews called it the Feast of Harvest or the Feast of Weeks. It is mentioned five places in the first five books—in Exodus 23, Exodus 24, Leviticus 16, Numbers 28, and Deuteronomy 16. It was the celebration of the beginning of the early weeks of harvest. In Palestine there were two harvests each year. The early harvest came during the months of May and June; the final harvest came in the Fall. Pentecost was the celebration of the beginning of the early wheat harvest, which meant that Pentecost always fell sometime during the middle of the month of May or sometimes in early June.
There were several festivals, celebrations, or observances that took place before Pentecost. There was Passover, there was Unleavened Bread, and there was the Feast of Firstfruits. The Feast of Firstfruits was the celebration of the beginning of the barley harvest. Here's the way you figured out the date of Pentecost. According to the Old Testament, you would go to the day of the celebration of Firstfruits, and beginning with that day, you would count off 50 days. The fiftieth day would be the Day of Pentecost. So Firstfruits is the beginning of the barley harvest and Pentecost the celebration of the beginning of the wheat harvest. Since it was always 50 days after Firstfruits, and since 50 days equals seven weeks, it always came a "week of weeks" later. Therefore, they either called it the Feast of Harvest or the Feast of Weeks.
This year, Pentecost will be on June 9th, 2019 observed on the seventh Sunday after Easter (April 21st).
Why is Pentecost Significant to Christianity?
Modern Christians observe Pentecost as a holiday, not to celebrate a wheat harvest, but to remember when the Holy Spirit invaded the Church in Acts 2.
1. The Holy Spirit filled the Church with power and added 3,000 new believers.
The account in Act 2 reports that, after Jesus ascended in to heaven, Jesus’ followers were gathered together for the Feast of Harvest (aka Pentecost), and the Holy Spirit “filled the whole house where they were sitting” (Acts 2:2). “All of them were filled with the Holy Spirit and began to speak in other tongues as the Spirit enabled them” (Acts 2:4). This strange occurrence drew a large crowed, and Peter stood up to speak to them about repentance and the gospel of Christ (Acts 2:14). By the end of the day that the Holy Spirit came, the Church grew by 3,000 people (Acts 2:41). This is why Christians still celebrate Pentecost.
John Gill expresses the significance in his commentary:
“Through this baptism of the Holy Ghost and fire, the apostles became more knowing, and had a greater understanding of the mysteries of the Gospel, and were more qualified to preach it to people of all nations and languages.”
2. The Holy Spirit was prophesied in the Old Testament and promised by Jesus.
Jesus promised the Holy Spirit in John 14:26, who would be the Helper for his people.
“But the Helper, the Holy Spirit, whom the Father will send in My name, He will teach you all things, and bring to your remembrance all that I said to you.”
This New Testament event is also significant because it fulfills an Old Testament prophecy in Joel 2:28-29.
“And afterward, I will pour out my Spirit on all people. Your sons and daughters will prophesy, your old men will dream dreams, your young men will see visions. Even on my servants, both men and women, I will pour out my Spirit in those days.”
3 Historical Insights into Pentecost
There are three things you need to know about Pentecost that will help you understand Acts 2.
1. Pentecost was a pilgrim festival.
That meant that according to Jewish Law, all the adult Jewish men would come from wherever they were living to Jerusalem and personally be in attendance during this celebration.
2. Pentecost was a holiday.
No servile work was to be done. School was out. The shops were closed. It was party time.
3. There were certain celebrations and sacrifices and offerings which were prescribed in the Law for the day of Pentecost.
On Pentecost, the High Priest was to take two loaves of freshly baked wheat bread and offer them before the Lord. The wheat bread was made from the newly harvested wheat.
In short, Pentecost in the time of the Apostles was a great and grand harvest celebration. The streets of Jerusalem were clogged with thousands of pilgrims who had come from every point of the compass to celebrate the goodness of God and the bringing in of the wheat harvest.
Excerpted from "The P.U.I.H." from Keep Believing Ministries (used by permission).