The word “Pentecost” is derived from the Greek word for “fifty.” The Day of Pentecost, as recorded in Acts 2, occurred 50 days after Jesus’ resurrection and 10 days after His ascension. The day celebrates the sending of the Holy Spirit to the disciples following Jesus’ ascension. On the 50th day after the Sabbath of Passover week, the Jews celebrated a festival of thanksgiving for the harvest.

It was known by a number of different names:
Feast of Weeks (Ex. 34:22; Deut. 16:10)
Feast of Harvest (Ex. 23:16)
Day of First fruits (Num. 28:26)

The “Feast of Weeks” was the second-most important festival for the Jews. (The most important was Passover.) This explains why so many people from all over the Roman empire were in Jerusalem on the day when the Holy Spirit was sent (see Acts 2:8-11).

The Day of Pentecost is seen as the culmination of the Easter season. In many calendars, the day is listed as “Whitsunday.” This comes from the phrase “White Sunday,” and refers to practice of the newly baptized appearing in their white, baptismal garments on that day. The color of the day is red, symbolizing the tongues of fire that appeared on the apostles. In the early church, Jesus’ ascension and the sending of the Spirit were celebrated together. By the seventh century, Pentecost had become such an important festival that the whole week following was set aside to observe it. Law courts were not in session, and most work was forbidden. By the 12th century this was limited to only three days. In most European countries the Monday after Pentecost is still observed as a holiday.

“On the last and greatest day of the Feast, Jesus stood and said in a loud voice, “If anyone is thirsty, let him come to me and drink. Whoever believes in me, as the Scripture has said, streams of living water will flow from within him.” By this He meant the Spirit, whom those who believed in Him were later to receive. Up to that time the Spirit had not been given, since Jesus had not yet been glorified.”

“Holy Spirit, Light Divine, Shine upon this heart of mine;
Chase the shades of night away, Turn the darkness into day

Holy Spirit, all Divine, Dwell within this heart of mine;
Cast down ev’ry idol throne, Reign supreme, and reign alone.” (LSB 496:1, 4)