In chapter 23 of Leviticus, God summons the Israelites to worship and to celebrate seven annual feasts he has appointed. Walter Kaiser and Duane Garrett, in the NIV Archaeological Study Bible: An Illustrated Walk Through Biblical History and Culture,  explain that “during these holy convocations the priests presented sacrifices and other offerings, while the common people rested from their daily labor, sometimes fasting and sometimes feasting, and celebrated the seasonal blessings of God and the great redemptive moments in the lives of his people.”

Verse 5 kicks off the calendar of feasts with the Passover celebration. Kaiser and Garrett write:

Passover was celebrated on the fourteenth day of the first month of the Hebrew calendar (our late March to early April). According to Exodus 12:26–27, when subsequent generations inquired about the meaning of the Passover, they were to be told that it commemorated the manner in which the Lord had spared the Israelites the night he struck down the Egyptians’ firstborn sons (Ex 12:29–30 ).

Verses 6-8 describe the second feast, the Feast of Unleavened Bread. Kaiser and Garrett explain the significance of this festival:

The Feast of Unleavened Bread immediately followed the Passover (Ex 12:15–20) and lasted for one week. In the context of the exodus, eating bread without yeast signified hasty preparation and a readiness to depart. Yeast, which was studiously avoided during this feast, became a symbol of the pervasive influence of evil (cf. Mk 8:15 ; 1 Co 5:7–8 ).

Verses 9-14 describe the third spring festival, the Offering of Firstfruits.

The Offering of Firstfruits took place at the beginning of the barley harvest and signified Israel’s gratitude to and dependence upon God. It occurred seven weeks before [the next festival of] Pentecost, but there was also an offering of firstfruits associated with the Feast of Weeks or Pentecost . . . in celebration of the wheat harvest (Num 28:26–31).

Verses 15-22 describe the fourth spring festival, the Feast of Weeks, also called Pentecost.

The Feast of Weeks or Pentecost, occurring seven weeks after Passover, was a day of sacred assembly in which no work was allowed. Its primary focus was an expression of gratitude to God for the wheat harvest.

Verses 23-25 describe the first fall festival, the Feast of Trumpets.

The Feast of Trumpets, celebrated on the first day of the seventh Hebrew month, marked the end of the agricultural year. The seventh month was important because it also included two major holy days— the Day of Atonement and the Feast of Booths. The blasting of trumpets announced the commencement of this special month.

The Israelites associated the sound of trumpets with the theophany (visible manifestation of God) on Mount Sinai (Ex 19:16–19). Priests had also sounded trumpets prior to the destruction of Jericho (Jos 6:16), and trumpets were regularly used in Israel as a military signal (2 Sam 2:28). Thus, the blast of trumpets at the onset of the seventh month added to the solemnity of this sacred season.

Verses 26-32 describe the second fall festival, the Day of Atonement. Recall that the Day of Atonement was carefully examined in chapter 16 of Leviticus.

The Day of Atonement focused exclusively on atonement for the sins of the people. This ceremony took place on the tenth day of the seventh month. The high priest made atonement first for himself and his family and finally for all the people. Coming at the end of the agricultural year, this feast symbolized a final reckoning before God.

The seventh and final festival of the year is described in verses 33-44, The Feast of Tabernacles.

The Feast of Booths (also called the Feast of Tabernacles or Sukkoth) took place five days after the Day of Atonement (Num 29:12–40). The people “camped out” in small huts during this time in order to recall their temporary living quarters prior to taking the land of Canaan. This joyous week was a time of final celebration and thanksgiving for the year’s harvest (Deut 16:14–15 ). As the seventh and last annual feast, the Feast of Booths also represented the Sabbath principle.

The significance of these festivals is commonly missed by evangelical Christians. Consider the words of Gordon Wenham in The Book of Leviticus (The New International Commentary on the Old Testament):

Three of the principal OT feasts were taken over directly by the Christian Church: passover = Good Friday, unleavened bread = Easter, weeks = Pentecost. The three most significant events in Christ’s redemptive ministry coincided with these festivals. That they no longer always coincide today is because of various modifications to the calendar introduced since the first century.

The linkages between the feasts and Jesus’ life, death, and resurrection are unmistakable. Wenham explains,

The last supper seems to have been a passover meal (cf. Matt. 26:17), and John implies that our Lord was the true passover lamb whose bones were not to be broken (John 19:36 quoting Exod. 12:46; cf. John 19:14). Easter Sunday was probably the day the first sheaf was offered as a dedication offering. It is this ceremony of offering the firstfruits which led Paul to speak of Christ in his resurrection as the firstfruits (1 Cor. 15:23). Elsewhere he uses another aspect of the festival of unleavened bread as an incentive for holiness: as all yeast had to be cleared out of the home in preparation for the feast of unleavened bread, so sin must be put out of the Christian community.

When did the Holy Spirit come to the church? On the Feast of Weeks, or Pentecost. It occurred the 50^th day after Easter. Wenham continues:

Recognition of the OT background to these Christian festivals could perhaps give greater depth to Christian worship. When we celebrate Good Friday we should think not only of Christ’s death on the cross for us, but of the first exodus from Egypt which anticipated our deliverance from the slavery of sin. At Easter we recall Christ’s resurrection and see in it a pledge of our own resurrection at the last day, just as the firstfruits of harvest guarantee a full crop later on (1 Cor. 15:20,23). At . . . Pentecost we praise God for the gift of the Spirit and all our spiritual blessings; the OT reminds us to praise God for our material benefits as well.