The Feast of Weeks (Shavuot, or Pentecost) is always on the Sunday following the seventh Sabbath from the Feast of First Fruits (Resurrection Sunday). We do not celebrate it on the same day as the Jews in Israel, since they count the Sabbaths differently, and rarely is their holiday on a Sunday. But according to Leviticus 23, the Feast of Weeks always falls on a Sunday.
This holy day is the day when, 50 days after the Israelites were delivered from Egypt and the hand of Pharaoh, God gave Moses the Ten Commandments written on tablets of stone with His own finger. It is the day when the Holy Spirit was given to the church after the resurrection of Jesus, as recorded in Acts chapter 2, as was prophesied by Jeremiah in 31:31-34:
“Behold, the days are coming, declares the LORD, when I will make a new covenant with the house of Israel and the house of Judah, not like the covenant that I made with their fathers on the day when I took them by the hand to bring them out of the land of Egypt, my covenant that they broke, though I was their husband, declares the LORD. But this is the covenant that I will make with the house of Israel after those days, declares the LORD: I will put my law within them, and I will write it on their hearts. And I will be their God, and they shall be my people. And no longer shall each one teach his neighbor and each his brother, saying, ‘Know the LORD,’ for they shall all know me, from the least of them to the greatest, declares the LORD. For I will forgive their iniquity, and I will remember their sin no more.”
According to Leviticus 23, when we observe the Feast of Weeks, we are to do four things: 1) rest — it is one of the high holy Sabbaths; 2) give a first fruits (tithe) offering to the Lord and a freewill offering to the poor; 3) assemble together with other believers; and 4) feast! And I add, joyfully give thanks to the Lord for crucifying the old man, creating in us a new man after the likeness of Jesus Christ, and filling us with His Spirit so that we can walk in newness of life!