Leviticus 23:8
But ye shall offer an offering made by fire unto the LORD seven days: in the seventh day is an holy convocation: ye shall do no servile work therein. But ye shall offer an offering made by fire unto the LORD seven days: in the seventh day is an holy convocation: ye shall do no servile work therein.
The instruction belongs to the Feast of Unleavened Bread, which was kept for seven days. Its first day was set apart as a holy convocation on which no servile work was to be done. Its seventh day was likewise a holy gathering and holy convocation on which no servile work was to be done.
Offerings made by fire were to be presented to the Lord through the seven days, including on that seventh day. The appointed feast days were times to consider God's blessings and to bring offerings in grateful acknowledgment of them. They were also times of joyful remembrance and rejoicing in the freedom God had given Israel from bondage.