Shavuot  celebrates the Giving of the Torah on Mt. Sinai to Moses. It is the Jewish PENTACOST because it occurs 50 days after PASSOVER. The Jews counted 49 days after Passover until this day and called it the Counting of the Omer as it coincided with the BARLEY harvest. When the disciples were together in the upper room this was the FEAST they were celebrating. This was when the Ruach Ha’Kodesh was given after the ascension of YaHushuWaH Ha’ Meshiach to heaven. It was also the first day that a WHEAT offering could be made unto YaHuWaH.