Yahweh, our Father, in speaking to His people through His Word, Yahushua, used parables and similitudes (see here for all of Yahushua's (Jesus') parables) to make His Word more clear to believers, yet hidden to others. He likened His plan of redemption (which is the Kingdom of Yahweh) to a harvest.

And he said, So is the kingdom of Yahweh, as if a man should cast seed into the ground; And should sleep, and rise night and day, and the seed should spring and grow up, he knoweth not how. For the earth bringeth forth fruit of herself; first the blade, then the ear, after that the full corn in the ear. But when the fruit is brought forth, immediately he putteth in the sickle, because the harvest is come. Mark 4:26-29

When the Bible speaks of the harvest it is based on the yearly harvest cycle in Israel. We must understand that cycle to understand the similitude. Yahweh's audience (being largely agrarian) intimately understood this cycle. But we must study it before studying the likeness.

First the seed is planted and the vines prepared.

And he spake many things unto them in parables, saying, Behold, a sower went forth to sow; And when he sowed, some seeds fell by the way side, and the fowls came and devoured them up: Some fell upon stony places, where they had not much earth: and forthwith they sprung up, because they had no deepness of earth: And when the sun was up, they were scorched; and because they had no root, they withered away. And some fell among thorns; and the thorns sprung up, and choked them: But other fell into good ground, and brought forth fruit, some an hundredfold, some sixtyfold, some thirtyfold. Matthew 13:3-8

Hear another parable: There was a certain householder, which planted a vineyard, and hedged it round about, and digged a winepress in it, and built a tower, and let it out to husbandmen, and went into a far country: Matthew 21:33

The three feast days (Passover, Pentecost and Atonement) correspond to three separate harvests in Israel and ultimately to the similitude of three harvests of people to be glorified. Each harvest crop represents a different class of people at a different time.

BARLEY

Barley, ripens first, at the time of Passover, so is harvested first. It represents the overcomers. This includes the Messiah, Himself and the wise virgins who go to Heaven at the 2nd coming of Yahushua, the Christ, some being resurrected and some never seeing death; The tares will first be removed (dying at the sight of the returning King), then the barley will be harvested.

WHEAT

Wheat, ripens 7 weeks plus 50 days later, at the time of Pentecost so is harvested after the barley. The wheat represent the rest of the believers who were NOT overcomers (foolish virgins, who looked for the bridegroom's coming, but were deficient - lacked sufficient oil). They are resurrected after the millennium.

GRAPES

Grapes, don't ripen until the end of the growing season, in the fall at the time of Ingathering. They are harvested last, and represent the harvest of unbelievers.

The husbandman (the Father) is patient and will wait for the early rain (for planting) and the latter rain (for spring harvest).

Be patient therefore, brethren, unto the coming of the Master. Behold, the husbandman waiteth for the precious fruit of the earth, and hath long patience for it, until he receive the early [rain after the fall harvest at planting time] and latter rain [rain that plumps the grain of the spring harvest]. James 5:7

Sowing seed and planting a vineyard are in anticipation of a future abundant harvest. What are the harvest cycles in Israel?