Christians may confuse the barley and wheat, but they believe and accept the salvation of both. However, they are reluctant to accept salvation for the grapes. This is generally expressed in three objections: belief, fairness and freewill. Each will be briefly touched below, but I hope to someday write a more complete explanation.
BELIEF IN YAHWEH'S ABILITY TO SAVE
Christians believe what they have been taught, not necessarily what Christ has told us. We have been taught that the wicked will either suffer in hell for eternity or will be annihilated, as if they never existed. There are many proponents and arguments on each side. But Christ explicitly says that He is "mighty to save" (Isaiah 63:1) and that He will NOT destroy the grapes in cluster. (Isaiah 65:8). Both verses are from the same prophecy. Christ is either telling the truth or lying.
I acknowledge that many verses SOUND as if the false doctrines of eternal hellfire or annihilation are true. Some are due to purposeful editorial license of scriptural translations, some are due to misinterpretation based on years of misunderstanding and all are due to our misunderstanding of Yahweh's character, mercy, love and power.
Briefly, to be saved, ALL must die and be reborn (John 3:3). ALL must go through the fire (Mark 9:49). ALL must wear their robe of righteousness (Matthew 22:11-13). The death and rebirth takes place either on this earth before the barley harvest and before the first death (preferable), or after the millennium and after the first death and resurrection (which is why it is called the second death).
Revelation 2:11
He that hath an ear, let him hear what the Spirit saith unto the churches; He that overcometh shall not be hurt of the second death.
The overcomers are the barley harvest. This verse tells us (by inference and omission) that both the wheat and the grapes WILL go through the second death process. Only the overcomers (barley harvest) are mentioned as being saved without going through the second death.
Most Christians believe that the second death is eternally fatal, but we must remember that Christ suffered the second death in His sacrifice for our salvation, yet was glorified. He did it on his own, but the grapes and wheat will accomplish it through Him.
Once we realize that the fire is figurative (spiritual - see Lake of Fire) for all (barley, wheat and grapes) it is easier to understand.
Once we realize that the death and rebirth are spiritual for all (barley, wheat and grapes) it is easier to understand. (see Purification of the Harvest)
Whole books have been written on this subject, so I don't hope to do any more than stimulate thought processes here.
FAIRNESS
The next objection is an expressed lack of fairness for the wicked to be saved. First, the Bible makes it clear, only the righteous will be glorified. This whole study is about the required robes of righteousness and how they are obtained. To be very clear, the wicked will not be glorified (even though Christ died to save us while we were yet sinners. Romans 5:8). But, if they are (eventually) reborn, what objection can remain? If Christ can make them righteous, doesn't He have the right to redeem and restore and glorify them?
Besides, ALL have sinned and come short, so how can you or I pretend to be any better than the worst sinner? We need to say, as Paul did:
1 Timothy 1:15
This is a faithful saying, and worthy of all acceptation, that Christ Jesus came into the world to save sinners; of whom I am chief.
Christ answered the issue of fairness in two of His parables. In the Prodigal Son, we see the prodigal's brother complaining about fairness. He had stayed home and worked hard and obeyed all his father's commands. He hadn't spent his father's inheritance on riotous living. It wasn't fair that his father was happy to see his lost son return and make a feast for him.
Christ acknowledged the brother's feelings, but ignored them as irrelevant. What was important was "for this thy brother was dead, and is alive again; and was lost, and is found."
The other parable is about the Workers in the Vineyard. Some workers worked only a short amount of time for the same pay as those who worked all day. The master asked if they hadn't been given what was promised? and didn't He have the right to do as he wanted?
FREEWILL
But, what if they don't WANT to be saved? This objection assumes man has freewill. He does NOT.
See Predestination - The Myth of Freewill
We must learn to understand and acknowledge Yahweh's love, mercy, power, ability and will to save. He has a plan to save all (1 Timothy 2:3-4, 1 Timothy 4:9-11, Philippians 2:10-11, Acts 3:21, John 17:12, John 12:32, Luke 3:6, Revelation 15:4, Ephesians 1:9-11 and many other verses, to be presented in a separate study) and He is "mighty to save".
That plan includes obtaining our robes of righteousness. How we obtain them depends on His purpose for our lives and when we are harvested. Our only task is to accept His will.