Under the Law of Moses, Israel was commanded to celebrate the Feast of Weeks seven weeks after the Feast of Unleavened Bread.
The Feast of Weeks was the second major feast in the Israelite callendar, following Passover / Feast of Unleavened Bread. Eventually the Feast of Weeks became known as Pentecost because it was 50 days after the Feast of Unleavened Bread.
9 “You shall count seven complete weeks for yourself; begin to count the seven weeks from the time you begin to put the sickle to the grain. 10 Then you shall keep the Feast of Weeks to the Lord your God, and according to your ability you may offer whatever you wish, as the Lord your God blessed you. 11 You shall rejoice before the Lord your God, you and your son and daughter, your male servant and female servant, the Levite who is within your cities, the resident alien and the fatherless and the widow who are among you, at the place where the Lord your God chooses for His name to be called upon there. 12 And you shall remember you were a servant in the land of Egypt, and you shall be careful to observe these commandments.Deuteronomy 16:9-12 OSB
9 Again the Lord spoke to Moses, saying, 10 “Speak to the children of Israel, and say to them, ‘When you come into the land I give you and reap its harvest, you shall bring a sheaf of the firstfruits from your harvest to the priest. 11 He shall offer the sheaf before the Lord, to be accepted on your behalf; on the morning after the first day the priest shall offer it. 12 Then you shall offer on that day on which you offer the sheaf a sheep of the first year, without blemish, as a whole burnt offering to the Lord. 13 Its grain offering shall be two-tenths of an ephah of fine flour mixed with oil, a sacrifice to the Lord, for a sweet aroma to the Lord; and its drink offering shall be of wine, one-fourth of a hin. 14 You shall eat neither bread nor roasted fresh ears until the same day you have offered gifts to your God; it shall be an ordinance forever throughout your generations in all your dwellings.
15 ‘Then you shall count for yourselves from the morning following the Sabbath day, from the day you brought the sheaf of the deposit, seven full weeks. 16 Count fifty days to the day after the seventh Sabbath; then you shall offer a new grain offering to the Lord. 17 You shall bring from your dwellings two deposit loaves of two-tenths of an ephah of fine flour. They shall be baked with leaven. They are firstfruits to the Lord. 18 Then you shall offer with the bread seven lambs of the first year without blemish, one young bull, and two rams without blemish. They shall be a whole burnt offering to the Lord, with their grain offering and drink offerings, a sacrifice for a sweet aroma to the Lord. 19 After this, you shall sacrifice one kid of the goats as a sin offering, and two lambs of the first year as a sacrifice of a peace offering, with the loaves of the firstfruits. 20 The priest shall deposit them with the loaves of the firstfruits as a deposit offering before the Lord, with the two lambs. They shall be holy things to the Lord; and for the priest who presented them, his shall they be. 21 Then you shall proclaim the same day as a holy convocation for you. You shall do no service work on it. It shall be an ordinance forever in all your dwellings throughout your generations.Leviticus 23:9-21 OSB
26 ‘Then on the day of new grain, when you bring a new grain offering to the Lord at your Feast of Weeks, you shall have a holy convocation. You shall do no service work. 27 You shall offer whole burnt offerings as a sweet aroma to the Lord: two young bulls from the oxen, one ram, and seven unblemished male lambs in their first year, 28 with their grain offering of fine flour mixed with oil: three-tenths of an ephah for each bull, two-tenths for the one ram, 29 and one-tenth for each of the seven male lambs; 30 also one young male of the goats, to make atonement for you. 31 In addition to the regular whole burnt offering—be sure they are unblemished—you shall offer to Me their grain offering with their drink offerings.Numbers 28:26-31 OSB
Details of the Feast of Weeks:
- Celebrated seven weeks after putting the sickle to grain
- Offer a sheaf of the firstfruits of grain, according to how they were blessed
- Bring the offering to the priest, eventually at Jerusalem
- Sacrifice seven lambs without blemish as a burnt offering, two young bulls, and two rams
- Bring two loaves of leavened bread from a mixture of fine flour and oil, and some wine for drink offerings
- Sacrifice a goat for a sin offering (to make atonement)
- Sacrifice two lambs as a peace offering along with the loaves
- This fiftieth day, Pentecost, was a holy assembly (Sabbath) with no work to be performed
- Israel to wait until after these offerings to eat bread from their harvest