I am not sure if what i think it says is correct? correct me if im wrong, or misunderstood, it is as if saying that the Day of Christ has already arrived to the fully converted, basically it is saying that Day of Christ will not come to a certain person till they are fully converted.
Excerpt from Lake of Fire Part 14 (http://bible-truths.com/lake14.html):
THE DAY OF THE LORD AND II THESSALONIANS II
Most of us not unlike the Thessalonians of Paul’s day are aware of a prophetic time spoken by the prophets known as "The Day of the Lord." The Thessalonians knew somewhat of this day and what it portended, as Paul spoke to them earlier about it. Now he has to tell them in this second epistle,
"That ye be not soon shaken in mind, or be troubled neither by spirit, nor by word, nor by letter as from us, as that THE DAY OF CHRIST is at hand" (II Thes. 2:2).
Never forget that Jesus Christ IS ‘The LORD,’ and so the Day of Christ and the Day of the Lord both represent the Son of God.
Notice what Paul had instructed them in his first epistle concerning the coming of the Lord:
"…and how ye turned to God from idols to serve the Living and True God; And to wait for His Son from heaven, Whom He raised from the dead, even Jesus, which delivered us from the wrath to come" (I Thes. 1:9b-10).
Paul tells them of his suffering:
"For yourselves, brethren, know our entrance in unto you, that it was not in vain: But even after that we had SUFFERED before, and were SHAMEFULLY ENTREATED, as ye know… with MUCH CONTENTION
(I Thes. 2:1-2). Then Paul speaks of their suffering and the reason for sending Timothy to them:
"That no man should be moved by THESE AFFLICTIONS: for yourselves know that we are appointed thereunto" (I Thes. 3:3).
Paul states that:
"Therefore, brethren, we were comforted over you in all our AFFLICTION and DISTRESS by your faith" (I Thes. 3:7).
And so Paul tells them of his afflictions, and also acknowledges their afflictions. Again Paul assures these Thessalonians that:
"For yourselves know perfectly that THE DAY OF THE LORD so comes as a thief in the night… For God has NOT appointed us to wrath, but to obtain salvation by our Lord Jesus Christ" (I Thes. 5:2 & 9).
Well Timothy reported back to Paul that they were having even more tribulations and persecutions to the point that they were thinking that they must be in that period of time of "The Day of the Lord," and that they themselves were suffering wrath from God.
Once more Paul acknowledges these tribulations and suffering:
"So that we ourselves glory in you in the churches of God for your patience and faith in ALL YOUR PERSECUTIONS AND TRIBULATIONS THAT YE ENDURE" (II Thes. 1:4).
But rather than wrath from God, Paul assures them that this suffering is really a token of God’s righteous judgment and that God will be punishing those who are persecuting them:
"Which [suffering] is a manifest token of the righteous judgment of God, that ye may be COUNTED WORTHY of the kingdom of God, for which ye also suffer: Seeing it is a righteous thing with God recompense tribulation to them that TROUBLE YOU" (II Thes. 1:5-6).
Then Paul gives them one more giant promise of rest from all of these sufferings:
"And to you [and to US as well] who are troubled REST with us, when the Lord Jesus shall be revealed from heaven with His mighty angels, In flaming fire taking vengeance on them that know not God, and that obey not the gospel of our Lord Jesus Christ: Who shall be punished with everlasting destruction [eonian extermination] from the presence of the Lord, and from the glory of His power; When He shall come to be glorified in His saints, and to be admired in all them that believe (because our testimony among you was believed) IN THAT DAY" (II Thes. 1:7-10).
And next we come to the Scriptures of our present study. Paul comforts them in their persecutions and tribulations. He assures them that endurance in faith will account the worthy to be in the Kingdom of God, and that they will have rest at the coming of our Lord to be glorified in His saints and admired in ALL THAT BELIEVE. This is the way of the believer leading up to the coming of the Lord and the "Day of the Lord," when all will be changed and glorified. But Paul tells them that that day is not here yet.
Listen carefully: Generation after generation after generation of believers and saints of God have lived, suffered and been persecuted, and then DIED. This "Day of Christ" or "Day of the Lord" not only did not come in their lifetime, but it will not be a reality to any of them WHEN IT DOES COME, unless something else happens in their lives FIRST!
Unless this experience happened to them in their lifetime, whenever they lived, they will not be in the First Resurrection and see the Coming of the Lord in the Day of the Lord. Something had to have happened to them—all of them. Something HAS to happen to YOU—ALL OF YOU who expect to see the Coming of the Lord and the Day of the Lord and be accounted worthy to be in The Kingdom of God. Yes, we already read in II Thes. 1:10, "When He shall come to be glorified in His saints…" And He will be glorified in all His saints at that time, but not unless something has happened in all of His saints FIRST!
Until and unless the thing that I am going to mention next is an accomplished FACT in your PRESENT life, you will not see The Coming of the Lord, neither will you be in the First Resurrection of spiritual rest and glorification. I kid you not, this is deep and heavy stuff!
BEFORE THE DAY OF THE LORD CAN COME TO YOU
Here then is what must be accomplished in your life before you die:
"Wherefore also we pray always for you, that our God would count you worthy of this calling, and fulfill all the good pleasure of His goodness, and the work of faith with power: THAT the Name of our Lord Jesus Christ may be GLORIFIED IN YOU [IN YOU], and YE IN HIM, according to the grace of our God and the Lord Jesus Christ" (II Thes. 1:11-12)!!
How then does our Apostle Paul tell us this MUST be accomplished? What must happen? What must we do? Or rather what must Jesus do IN US? Here is the Scriptural answer:
"Now we beseech YOU, brethren, by the coming of our Lord Jesus Christ, and by our gathering together unto Him.
That ye be not soon shaken in mind or be troubled, neither by spirit, nor by word, nor by letter as from us, as that THE DAY OF CHRIST [The Day of the Lord] is at hand [FOR YOU...].
Let no man deceive YOU by any means: for that day shall not come [TO YOU…] except there come a FALLING AWAY FIRST [BY YOU…], and the man of sin be revealed the son of perdition [IN YOU…TO YOU…]; Who opposes and exalts himself above all that is called God, or that is worshipped [IN YOU…]; so that he as God sits in the temple of God [‘which temple YE ARE’ II Cor. 6:16] showing himself that HE IS [YOU ARE / I AM] a god
Remember ye not, that when I was yet with YOU, I told YOU these things?
And now ye know what withholds [is restraining, is detaining—‘the falling away FIRST’] that he [‘the man of sin be revealed, the son of perdition’—YOU…] might be revealed in his time [in YOU and TO YOU—individually, not collectively] in his time [‘his {particular} time’]—FOR YOU and FOR ME and for ALL BELIEVERS IN ALL GENERATIONS UNTIL JESUS COMES TO US ALL, COLLECTIVELY, AS THE MANIFEST SONS OF GOD]."
Long before Jesus can have a COMPANY of manifest SONS and DAUGHTERS of God, there has to be individual begettals by the Holy Spirit of God in chosen individuals in every generation leading up to the coming of the Lord at the end of this age.
"For the mystery [secret, hidden truth] of iniquity [lawlessness] does already work [‘is inwardly working’ The Emphasized New Testament: A New Translation (J. B. Rotherham)]: only he who now lets will let [‘only he who restrains will do so’], until he be taken out of the way.
And then shall that Wicked [Lawless One] be revealed IN [IN YOU] and TO YOU, whom the Lord shall consume with the spirit [breath] of His mouth, and shall destroy with the brightness of his coming;
Even him [not original], whose coming [the man of sin called son of perdition IN YOU] is after the working of Satan with all power and signs and lying wonders" (II Thes. 2:1-9).
The Day of the Lord is not fulfilled until the end of this age [Matt 24, Mark 13, Luke 21].
Hope this helps,
Marques