I'll divide into subarguments to keep things focused
They are not a part of the Church, but are the redeemed who had failed to seek the new birth before Christ took the Church from the earth, leaving behind those who were not prepared.
All saints are tribulation saints. The body of Christ is not divided.
The ones not prepared are the unrighteous tares in the churches, that name Christ and repent not to depart from their iniquity. They are appointed with the hypocrites of the earth, and have no more space to repent. They are the dead limbs cut off and ready only for the punishing fire.
Mat 24:48
But and if that evil servant shall say in his heart, My lord delayeth his coming;
The lord of that servant shall come in a day when he looketh not for him, and in an hour that he is not aware of, And shall cut him asunder, and appoint him his portion with the hypocrites: there shall be weeping and gnashing of teeth.
Rev 2:21
And I gave her space to repent of her fornication; and she repented not. Behold, I will cast her into a bed, and them that commit adultery with her into great tribulation, except they repent of their deeds.
And I will kill her children with death; and all the churches shall know that I am he which searcheth the reins and hearts: and I will give unto every one of you according to your works.
When the righteous wheat are resurrected and ascend to the Lord in the air, then the great tribulation of the Lord's wrath over the earth begins. All inhabitors are the unrepented, and Scripture says none will repent during the plagues of the Lord.
Rev 9:20
And the rest of the men which were not killed by these plagues yet repented not of the works of their hands, that they should not worship devils, and idols of gold, and silver, and brass, and stone, and of wood: which neither can see, nor hear, nor walk:
Rev 16:9
And men were scorched with great heat, and blasphemed the name of God, which hath power over these plagues: and they repented not to give him glory. And blasphemed the God of heaven because of their pains and their sores, and repented not of their deeds.
His great plagues and destruction of the armies gathered against the Lamb and His saints around Judea, will kill very many on earth, more thanj ever before in one season.
Psa 2:7
I will declare the decree: the LORD hath said unto me, Thou art my Son; this day have I begotten thee.
Ask of me, and I shall give thee the heathen for thine inheritance, and the uttermost parts of the earth for thy possession. Thou shalt break them with a rod of iron; thou shalt dash them in pieces like a potter's vessel.
Rev 19:15
And out of his mouth goeth a sharp sword, that with it he should smite the nations: and he shall rule them with a rod of iron: and he treadeth the winepress of the fierceness and wrath of Almighty God.
However, there will be those of the nations remaining alive to be ruled by the Lord. He will first judge between sheep and goats, with the sheep not being saints, being sinners with showing kindness and care in times of trouble. These will be saved by the King and enter into His kingdom of heaven on earth.
The unfeeling goats on earth will be executed by sentence of the King.
Eph 4:17
This I say therefore, and testify in the Lord, that ye henceforth walk not as other Gentiles walk, in the vanity of their mind, Having the understanding darkened, being alienated from the life of God through the ignorance that is in them, because of the blindness of their heart:
Who being past feeling have given themselves over unto lasciviousness, to work all uncleanness with greediness.
Not all unbelieving sinners are the world's reprobate evil-doers in their manners, even as not all believers naming Christ are His doers of His righteousness.
The scriptures clearly show to us that there is a difference between the Church and the tribulation saints.
Once again, all saints on earth are tribulation saints, and the godly shall suffer persecution from angry sinners.
So long as this is denied, then the error of dividing Christ's body will continue.
If a prophetic division is made between the resurrected church in the air, and any saints alive on earth suffering tribulation of the Lord's own wrath, then the Scripture is broken: None of Christ's saints are ever appointed to suffer His wrath on earth.
The Lord's wrath is only for the unrepented and unrighteous, whether naming His name or not.
The only 'Christians' on earth appointed to His wrath at His coming again, are the hypocrite tares separated from His good wheat at the harvest.
They are not one and the same,
Christ's body is not divided. Any doctrine and prophecy seeking to do so, is false.
Rom 12:5
So we, being many, are one body in Christ, and every one members one of another.
1Co 1:13
Is Christ divided? was Paul crucified for you? or were ye baptized in the name of Paul?
1Co 1:10
Now I beseech you, brethren, by the name of our Lord Jesus Christ, that ye all speak the same thing, and that there be no divisions among you; but that ye be perfectly joined together in the same mind and in the same judgment.
The unity of Christ's body specifically includes during time of judgment of the Lord.
as can be seen in the reward differences alone, not to mention that the Church is not standing among those who came from the tribulation.
What Scripture?
There is one equal reward for all enduring saints: The crown of life, righteousness, and glory of the Lord.
Ministerial rewards are cities during His Millenium.