Deuteronomy 16:9
Seven weeks shalt thou number unto thee: begin to number the seven weeks from such time as thou beginnest to put the sickle to the corn. Seven weeks shalt thou number unto thee: begin to number the seven weeks from such time as thou beginnest to put the sickle to the corn.
The seven weeks are to be numbered from the time the sickle is first put to the corn, marking the beginning of the grain harvest. The count closes at Pentecost, which comes seven weeks after Passover. That same endpoint is fifty days after the offering of the firstfruits.
Pentecost is also called the Feast of Harvest and the Feast of Weeks. The numbering belongs among the appointed religious seasons when the people were to assemble before God, lay aside unnecessary work, and consider His blessings. These seasons called for gratitude expressed through offerings and rejoicing.
The feast itself lasted one day devoted to religious service. It expressed gratitude to God for grain prepared as food, represented by two leavened loaves presented to Him. At the feast the people brought the firstfruits of the harvest to the temple, acknowledging their dependence on God. In doing so they returned gifts to support His cause.
The believers who received the Holy Spirit at Pentecost were the firstfruits of the Christian church.