Shavuot, meaning weeks, (also known as Pentecost, meaning 50) comes from Lev 23:16. In Acts 2 we read that there were thousands of Jews in Jerusalem celebrating Pentecost and remembering how God appeared to them on Mt. Sinai in fire and glory 1500 years earlier, giving them His law on the tablets of stone (Exo. 19:16-19). The disciples encountered this as God filled them with His Holy Spirit and wrote His law in their hearts. This was the fulfillment of what the prophets spoke of in Ezk 36:26 “I will give you a new heart and put a new spirit within you”. Final atonement for sin was accomplished at Passover and the gift of the Holy Spirit was given at Pentecost-Shavuot. Hallelujah!
This feast takes place fifty days after the feast of First Fruits (Leviticus 23:15-16; First Fruit’s is also the day that Yeshua rose from the dead). This feast also came to be associated with the day that the LORD gave the Law to the children of Israel at Mt. Sinai. In Acts 2, as Yeshua’s disciples were remembering how the God of Israel manifested Himself in fire at Mt. Sinai, they suddenly encountered that same fire as the God of Israel filled them with His Holy Spirit.