Barley, wheat, and grapes are all harvested differently.

Barley has a soft shell. You cannot step on barley or you'll 'crush'
it. Harvesters take a 'fan' (it looks like a pitch fork) and they gather the barley
together and throw it up in the air. The 'wind' (Holy Spirit) separates the outer
shell from the meat which is the barley itself and they collect the barley and
bring it in. The barley harvest is a picture of the saints whose hearts are
'tender' who do not have to be separated as wheat and chaff. Revelation 4:1
represents the rapture of the church.

The wheat and tares grow together until the end of the age and are not
separated lest the wheat be uprooted with the tares. This represents the
Second Coming of Jesus and the wheat harvest will have to endure some
"heat".

The word 'out' is called, in Latin, a 'tribulum' from which we get the word,
'tribulation'. There is no 'tribulum' used at Passover with the barley. A
'tribulum' is however used for the wheat and grape harvests. Separating the
wheat and tares is considered the next harvest and will be those who were not
ready when the church was raptured, but may have to die for their newly
found faith during the tribulation. It is absolutely essential to NOT take the
mark of the beast at this time which will be the only way to buy and sell.

The grape harvest represents the last group of people to repent and humble
themselves before God. That group of people will have to endure the most
horrendous time on Earth ever:

And another angel came out from the altar, which had power over fire; and
cried with a loud cry to him that had the sharp sickle, saying, Thrust in thy
sharp sickle, and gather the clusters of the vine of the earth;
for her grapes
are fully ripe
. And the angel thrust in his sickle into the earth, and gathered
the vine of the earth, and cast it into the great winepress of the wrath of
God.
Revelation 14:18,19
Meaning of the Barley, Wheat, & Grape Harvests