The Jews celebrated seven annual Feast Days or Holy Days during the year, three in the spring (Passover, Days of Unleavened Bread, and Pentecost) and four in the autumn (Trumpets, Atonement, Tabernacles and the Last Great Day). These annual Holy Days are found in Leviticus 23, and are described by Paul as days which were shadows of better things to come, and he claimed that the body, i.e. the body which cast the shadows, was Christ (Colossians 2:16-17). So, when Jesus mentions the time of the harvest in Matthew 13:30 and 39, it shouldn’t have been difficult for the Apostles to see how the end of the age correlates with the time of the harvest, resurrection, judgment, and their gathering into the presence of God in his Kingdom, because these very things are clearly expressed in the celebration of Israel’s fall Festivals.
Jesus fulfilled the first three Holy Days during his public ministry, and this is taught in the New Testament. For example, Paul describes Jesus as our Passover (1Corinthians 5:7), and Jesus claimed to be that unleavened bread (John 6:48), which Peter also mentions (1Peter 2:3). As for Pentecost, who would deny that the gift of the Holy Spirit isn’t the down payment of the believer’s inheritance in Christ, our hope of glory (Ephesians 1:13-14; Colossians 1:27).
Notice, however, that there is a separation between the fulfillment of the spring Holy Days and the fulfillment of the fall Holy Days. It is about three and one-half to four months, and this corresponds to the time between Pentecost 31 AD to cir. 66 to 70 AD or a period of about four decades (viz. Israel’s wandering in the wilderness for 40 years). This period also represents the generation Jesus mentioned that would take to fulfill all things (Matthew 23:36; 24:34). This generation (cir. 40 years) is the millennium of Revelation 20:4-6), because one cannot enter a strong man’s house, which refers to preaching the Gospel to the gentiles, and be successful, unless first the strong man is bound (cf. Matthew 12:29). So, one is able to see how Jesus’ words, concerning the harvest in Matthew 13 and concerning this generation in Matthew 23 and 24, dovetail into the work of salvation, as unveiled in Israel’s Feast Days.
In Rosh Hashanah or the Feast of Trumpets we see the resurrection of the dead (cf. Matthew 24:31), which also commences the judgment of the living and the dead (Revelation 20:11-15), and that culminates in the Day of Atonement (Yom Kippur), which, of course, relates to Jesus coming to judge Jerusalem and the Temple (cf. Matthew 24:30; 26:64).
Finally, we have the Feast of Ingathering (Tabernacles or Sukkoth), which points to believers being taken into the presence of God (Matthew 13:30), and the Last Great Day is the celebration of that undertaking (Matthew 13:43; Revelation 21:1-4). Remember that Jesus was describing the coming of the Kingdom of God, i.e. returning to the original Theocracy (1Samuel 8:4-7), when God alone would reign as King over his people (Matthew 13:24, 31, 33, 44, 45, 47).
Now, ask yourself this. Should we stone Sabbath breakers? Should we change the day we worship from Sunday to Saturday? Should we demand that Congress pass a law, making the days begin at sundown rather than midnight? How about the New Year, should it be in January or March, and should we pay our taxes in the spring or the fall? In other words, are the shadows (Colossians 2:16-17) still in force? Is the Old Covenant still the covenant that God honors to deal with mankind, or has the New Covenant arrived, and is it in force today between God and men?
If Jesus has truly fulfilled these days, and the New Testament claims he did fulfill three, but it also claims Jesus would shortly (in the first century AD) fulfill the remaining four. If these annual Feast Day have been fulfilled, then everything else is fulfilled. Either the Old Covenant is in force or it is not (cf. Matthew 5:17-18). Since there is no Temple, the Old Covenant cannot be in force. Moreover, since God has not dealt with the world through the Jews for the last (nearly) 2000 years, he must be dealing with mankind through the Gospel, and through the Church. Therefore, the resurrection has occurred, the judgment is complete, and we have been gathered into God’s presence, and he dwells with us today. If this is not so, then the Old Covenant, not the New Covenant, must be God’s modus operandi through which he deals with the nations.