Pentecost Sunday is traditionally a day that coincides with the Jewish Holiday of Shavuot (Leviticus 23:15-16). Shavuot is the festival that begins fifty (50) days after Passover and celebrates the bringing in of the “first fruits” of the harvest.
Christians celebrate Pentecost as the birth of the New Testament Church. A single day in history when God first poured out His Spirit and began to permanently indwell all those who believed in Jesus Christ as the Saviour.
The Bible says on that day, men from all nations were present and 3,000 believed on the name of Christ and were saved. (Acts 2:41)