Pentecost was originally an Old Testament festival, originated during the Exodus when it was called the Feast of the First Fruits, the Feast of the Weeks, Feast of the Latter Firstfruits (Shavuot, or the Feast of the Harvest (Leviticus 23:15-21), calculated as beginning on the fiftieth day after the beginning of Passover. This was one of the three annual festival seasons / Passover (Exodus 12:13) / The Days of Unleavened Bread (Exodus 12:15) / Pentecost (Leviticus 23:16-17).

Counting the days from the second day of Passover to Pentecost is called the "Counting of the Omer". A simple definition of "Pentecost" is fiftieth, or 50 days. Fifty is the number of jubilee or deliverance. In the Old Testament it was originally an agricultural festival celebrating and giving thanks for the "first fruits" of the early spring harvest (Exodus 23:16, 34:23). In fact, God was very specific about when this first harvest was to be started. The people were instructed to count seven weeks..."from the morrow after the Sabbath, from the day that ye brought the sheaf of the wave offering" (Leviticus 23:15) There was to be a small cutting of the grain (Barley) done by the priests on the day after the Sabbath during the Unleavened Bread festival (Passover). This small cutting was called the WAVE SHEAF (Leviticus 23:10-15) and it was waved before the Lord in the Tabernacle and later the Temple. This cutting of the grain and waiving it before God, once done, signified the end of the spring harvest of Barley and the beginning of the Wheat harvest.