The Feast of Pentecost signifies the New Testament believers' enjoyment of the outpoured Spirit as the aggregate of the rich produce of the resurrected Christ (Lev. 23:15-21; Acts 2:1-4, 32-33). The Feast of Pentecost came fifty days after the Feast of the Firstfruits, indicating that the outpoured Spirit is the aggregate of the rich produce of the resurrected Christ. The rich produce of Christ's resurrection includes the firstborn Son of God (Rom. 8:29; Heb. 1:6), the life-giving Spirit (1 Cor. 15:45b), the many sons of God (Rom. 8:29), and the new creation of God (2 Cor. 5:17). Christ was not the firstborn Son of God until He was resurrected. In resurrection He became the firstborn Son of God. Likewise, before the resurrection the life-giving Spirit was not yet (John 7:39); Christ produced the life-giving Spirit through His resurrection. Before the resurrection God did not have any sons besides His only begotten Son, but through Christ's resurrection we were all begotten of God to be His many sons (1 Pet. 1:3). These many sons became the many grains (John 12:24), who are the members of Christ, the brothers of Christ to constitute His Body (1 Cor. 10:17). All these items are in the aggregate of the rich produce of the resurrected Christ. The Feast of Pentecost is the totality of the produce of the Spirit through Christ's resurrection.
On the day of resurrection Christ was produced as the firstborn Son of God, the life-giving Spirit was produced, the many sons of God were produced, and the new creation was produced. However, the church was not yet produced. The church came into being on the day of Pentecost. This was the last item of all the produce of the resurrected Christ as the firstfruits offered to God. The totality, the aggregate, of these firstfruits is the outpoured Spirit.
The first four feasts are for the New Testament believers. The Feast of the Blowing of Trumpets, however, signifies God's calling together of Israel, His scattered, dispersed elect (Lev. 23:23-25; Matt. 24:31). This feast is for the coming Jews. The day of this feast has not yet come. It will come in the future. When Christ comes back, the angels will trumpet a call to gather His scattered people.
The Feast of Propitiation signifies God's propitiation for the repentant Israel (Lev. 23:26-32; Zech. 12:10—13:1). At the time Zechariah 12:10—13:1 is fulfilled, all the remnant of Israel will repent with weeping. A fountain of cleansing will be opened for them, and they will all be forgiven. That will be their Feast of Propitiation.
The Feast of Tabernacles signifies Israel's full enjoyment of the restored old creation in the millennium (Lev. 23:33-43; Zech. 14:16-21). This feast will usher in the new heavens and the new earth.