There are several things to realize about the Old Testament harvests and feasts.
The three harvests (Exodus 23:14-17) parallel the Crucifixion/Resurrection, Pentecost/The Church, and Christ’s Return (1 Corinthians 15:23-24).
The seven feasts of these harvests (Leviticus 23) correspond to the Church’s liturgical seasons: Advent, Christmas, Ordinary, Lent, Triduum, Easter, Ordinary.
The harvest seasons can be classified as such: the first (Spring/Summer) gave grain, the second (Summer) gave grapes, and the third (Summer/Fall) gave olives, figs, and more.
The first, of grains, was smaller in weight — because the other harvests were water-dense — but the biggest source of food, as it made up over 50% of the Jewish diet. Christ’s Crucifixion and Resurrection, even though He was merely one Man, are key in the same way.
Notable is that the second big harvest had grapes, and this was just after the wheat was brought in. Perhaps this is a Eucharist reference, relatable to the Church. At every event, bread and wine were crucial. These are also necessary to every Mass, at which they are confected into our new manna, which, like the old, sustains us until we reach the Promised Land. Christ’s Blood redeems and strengthens us. We already have the todah, the ultimate Sacrifice of thanksgiving and praise (CCC #1359-1361), which our rabbinical brethren await!
The third, which has the feast of tabernacles/booths, is important to the Second Coming. This can also be referred to as “the Ingathering”. The great festival involved imagery of water and light, which points toward baptism and Christ as the Light of the world (John 1:4-11). At His Return, Christ will reveal Himself to all as their rightful King (Zechariah 14:16), just as He revealed Himself to the Jews as the ultimate Teacher around this important feast (John 7:1-16). He will then perform His own, final Harvest and gather His flock to Himself (Matthew 13:24-30). At this, we will perpetually celebrate all of His wondrous deeds, just as the Israelites celebrated all of the year’s harvests (Deuteronomy 16:13-15).
Typology of the olives and figs is important, too. Olive oil was used to burn the lamps continually (Leviticus 24:2), and so the rule of God, at Christ’s Return at the olive harvest, will last forever. Jesus calls us to join Him under the security and sweetness of the fig tree and learn from Him (Micah 4:1-5, Zechariah 3:8-10) and be grafted into the eternal olive tree (Psalm 52:8, Romans 11:13-32).