He will come to judge His House first before the coming great tribulation.
1 Peter 4:17 For the time is come that judgment must begin at the house of God: and if it first begin at us, what shall the end be of them that obey not the gospel of God? 18 And if the righteous scarcely be saved, where shall the ungodly and the sinner appear? 19 Wherefore let them that suffer according to the will of God commit the keeping of their souls to him in well doing, as unto a faithful Creator.
I apply verse 19 to the promise that He will keep the souls of His unrepentant saints left behind to suffer the fire coming on the earth and the coming great tribulation as a result.
Here is one judgment on the church in getting left behind for not repenting from spiritual fornication in the Book of Revelations.
Revelation 2:18 And unto the angel of the church in Thyatira write; These things saith the Son of God, who hath his eyes like unto a flame of fire, and his feet are like fine brass; 19 I know thy works, and charity, and service, and faith, and thy patience, and thy works; and the last to be more than the first. 20 Notwithstanding I have a few things against thee, because thou sufferest that woman Jezebel, which calleth herself a prophetess, to teach and to seduce my servants to commit fornication, and to eat things sacrificed unto idols. 21 And I gave her space to repent of her fornication; and she repented not. 22 Behold, I will cast her into a bed, and them that commit adultery with her into great tribulation, except they repent of their deeds. 23 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. 24 But unto you I say, and unto the rest in Thyatira, as many as have not this doctrine, and which have not known the depths of Satan, as they speak; I will put upon you none other burden. 25 But that which ye have already hold fast till I come.
So that is why the pre great tribulation rapture will happen first; to judge the House of God for the Bridegroom to receive the abiding bride of Christ to the Marriage Supper above in Heaven and to cast away those not found abiding in Him to resurrect later on after the great tribulation.
Any saint that dies left behind, their spirit is with the Lord because they were saved by believing in the Lord Jesus Christ & that God raised Him from the dead after all.
2 Corinthians 5:6 Therefore we are always confident, knowing that, whilst we are at home in the body, we are absent from the Lord: 7 (For we walk by faith, not by sight:) 8 We are confident, I say, and willing rather to be absent from the body, and to be present with the Lord. 9 Wherefore we labour, that, whether present or absent, we may be accepted of him. 10 For we must all appear before the judgment seat of Christ; that every one may receive the things done in his body, according to that he hath done, whether it be good or bad. 11 Knowing therefore the terror of the Lord, we persuade men; but we are made manifest unto God; and I trust also are made manifest in your consciences.