To some it may come as a surprise to learn that Shavu’ot (Pentecost) is not originally a Christian festival.
The Hebrew word Shavu’ot means weeks. In Jewish tradition 7 is the perfect number (the number of creation) and 7 times 7, even more so. It is a week of weeks or 7×7 which is 49 days.
In ancient Israel, the number seven represented divine perfection. It was considered a powerful, unbreakable number because it could not be divided by common small numbers which people used to count on a single hand. The word for seven in Hebrew- sheva שֶׁבַע– is linked to shevua שְׁבוּעָה– an oath. When someone wanted to make a very strong promise, they would take an oath as though to say: “let the divinely perfect number seven be my witness that I…” (http://lp.israelbiblicalstudies.com)
This weekend we celebrate one of the three most important festivals on the Jewish calendar, Shavu’ot (The Festival of Weeks or Pentecost)—the other two being Pesach (Passover), and Sukkot (The Feast of Tabernacles).
At the time of Jesus, pilgrims would travel to the temple in Jerusalem to offer sacrifice on these three festivals. In fact, as we will hear in the first reading this Sunday, that’s why all of Jesus’ followers were gathered together in the upper room, to celebrate the Jewish festival of Shavu’ot:
“And when the day of Pentecost was fully come, they were all with one accord in one place. And suddenly there came a sound from heaven as of a rushing mighty wind, and it filled all the house where they were sitting. And there appeared unto them cloven tongues like as of fire, and it sat upon each of them. And they were all filled with the Holy Spirit, and began to speak with other languages, as the Spirit gave them utterance.” —Acts 2:1–5
To some it may come as a surprise to learn that Pentecost is not of Christian origin. The roots of Shavu’ot—both agricultural and historical—lie in ancient Israel.
Shavu’ot commemorates the time when God gave the Israelites the 10 Commandments, the way by which they were to live their lives. It is on that day that the Hebrews became a nation.
For the first Christians, Pentecost was the day they received the Holy Spirit, which dwells in the hearts of all believers, commanding the way they are to live their lives. Pentecost celebrates the unity of the first Christians and the birth of the Church.
adapted from http://www.massexplained.com