This festival had several names: Harvest, Weeks, and Pentecost (Gr. pentekostos, meaning "fiftieth"). It fell at the end of the spring harvest 50 days after Passover, namely, the day after the end of the seventh week. Pentecost means fiftieth day. This feast was a thanksgiving festival, and it lasted one day. The people offered God the first fruits of the harvest as a thank offering for His provision for their physical and spiritual needs.
The loaves of bread that the Israelites offered to God (v. 17) contained leaven.
". . . in them their daily bread was offered to the Lord, who had blessed the harvest . . ."259
These were common loaves of daily bread. The Israelites did not cook them specifically for holy purposes. They also presented other accompanying offerings (vv. 18-19).
God sent the Holy Spirit to indwell believers permanently as the firstfruits of God's blessings on Christians on the Pentecost following our Lord's death and resurrection (Acts 2).
This feast was primarily a time of appreciation for God's present provisions and care. Likewise our worship should include appreciation for these mercies as well.