Within the 7 day festival of unleavened bread, God later added another holiday called ‘the day of firstfruits/first sheaf wave offering’. It was a special day to be celebrated when Isreal finally settled into the promise land and grew their own crops. When they did; God commanded them to bring the the first sheaf of the early rippened barely (and early ripening spring grain crop) was to be selected from the field and brought to the Aaronite priest.
Leviticus 23:9-14
“The Lord said to Moses,‘Speak to the Israelites and say to them ‘When you enter the land I am going to give you and you reap its harvest, bring to the priest A sheaf of the first grain you harvest.’’”
Once it was harvested, the priest was to bring it before God to wave it before him as a wave offering, so God would accept this offering on all of Israel’s behalf:
Leviticus 23:11
“He is to wave the sheaf before the Lord so it will be accepted on your behalf;…”
God ordained this sacred first barely grain offering was to be offered the day after the sabbath day:
In this context, the weekly sabbath which was the first day of the festival of unleavened bread or the 15th of Nisan/Abib. So God puts this day AFTER the 15th so this was the 16th day:
Which in God’s calendar would be the first day of a new week (specifically the 3rd week of the first month). So God placed this special offering day inside the greater 7 day of the festival of unleavened bread specifically on the 2nd day of unleavened bread.
On this sacred day, God also commanded Israel to sacrifice special offerings: that is a perfect lamb, a grain offering and a wine offering:
Leviticus 23:12-13
“On the day you wave the sheaf, you must sacrifice as a burnt offering to the Lord a lamb a year old without defect, together with its grain offering of two-tenths of an ephah of the finest flour mixed with olive oil—a food offering presented to the Lord, a pleasing aroma—and its drink offering of a quarter of a hin [about 1 liter or quart] of wine.”
Until the first ripened barley grain of the early spring year was brought as an offering, NO NEWLY grown grain of that new year could be eaten by anyone in Israel. Only when the first fruits of the first rippened grain was brough before God as a wave offering could all other grains throughout the year be finally harvested and eatened by Isreal.
Leviticus 23:14
“You must not eat any bread, or roasted or new grain, until the very day you bring this offering to your God.”
Giving the first fruits of spring (specifically the barley) to God seems to be the reason behind the day of waved firstfruits in Israel. It purpose seems to be by giving the very first of their grain that ripens in spring to their God just like their firstborn son’s. It seems to greater symbolize how God comes first and get’s the best of the first fruits of all he has blessed them with.
God commanded this day to also begin a specific countdown (or really countup) to one final spring holyday separated from the rest he had commanded, this day was called (coming soon) Pentecost (or the day of first fruits).