I don't have 2 Thess 2:6-7 figured out yet but my guess is that Paul had taught them something out of Daniel on this and is reminding them about what he previously taught them. We should be able to study Daniel and pick up on what Paul taught them and figure out the mystery that he was explaining from the book of Daniel. Look for references that might relate to "the mystery of iniquity" the references to the man of sin, son of perdition, that Wicked, and the abomination of desolation, but the mention he that restrains or holds back, taken out of the way could be related to this ...
."At that time Michael, the great prince who protects your people, will arise. There will be a time of distress such as has not happened from the beginning of nations until then. But at that time your people--everyone whose name is found written in the book--will be delivered. I really think the answer is in Daniel. And Paul might have explained this to them. If you remember it was Michael that had to deal with the Prince of Persia in order for Gabriel to get to Daniel.
I don't understand it but there might be something related to "Holding back or restraining" that Michael will take care of when the mystery of iniquity is full, when "God has decided ENOUGH" or the cup of the sin of the gentiles is full. And Michael might already have specific orders to release something that allows THAT WICKED to go forth and have his moment of un restrained reign.
This is obviously all about a teaching from Daniel that he had previously explained to them. Unfortunately we were not there to hear it. However, God planned it this way. God wants us to trust the Holy Spirit to illuminate us as we study Daniel and get the same revelation that Paul had taught them. This is the challenge. Only a few will try, and only a few (in comparison to the masses) will have the condition of heart to understand.
4who opposes and exalts himself against every so-called god or object of worship, so that he takes his seat in the temple of God, proclaiming himself to be God. 5Do you not remember that when I was still with you I told you these things? 6And you know what is restraining him now so that he may be revealed in his time. 7For the mystery of lawlessness is already at work. Only he who now restrains it will do so until he is out of the way. 8And then the lawless one will be revealed,
I think I am on the right trail. I just have to give it more attention. I think what I have presented is very close to the explanation.
God's holy ones, the church is restraining him. But he wants to deceive them into thinking, they do not need to be concerned about him, and restrain him, as they will be raptured before his lawlessness is revealed. Daniel teaches us in Daniel 8:24 that the revealed lawless one will also destroy the might of God's holy ones.
II Thessalonians 2 (NKJV)
1Now, brethren, concerning the coming of our Lord Jesus Christ and our gathering together to Him, we ask you, 2not to be soon shaken in mind or troubled, either by spirit or by word or by letter, as if from us, as though the day of Christ had come. 3Let no one deceive you by any means; for that Day will not come unless
the falling away comes first, and the man of sin is revealed, the son of perdition, 4who opposes and exalts himself above all that is called God or that is worshiped, so that he sits as God in the temple of God, showing himself that he is God.
5Do you not remember that when I was still with you I told you these things? 6And now
you know what is restraining, that he may be revealed in his own time. 7For the mystery of lawlessness is already at work; only He who now restrains will do so until He is taken out of the way. 8And then the lawless one will be revealed, whom the Lord will consume with the breath of His mouth and destroy with the brightness of His coming.
You are right, we look to Daniel for the answer to this mystery, it is when God's holy people is out of the way, out of the way, removed from any position of power or influence. The Church fathers had it figured out, and like Christ Yeshua, taught their flock to be prepared for the post-tribulation, pre-millenium return of Christ Yeshua. Imagine Christ Yeshua, teaching his apostles to go out and proclaim the gospels among the nation, and then added false hope telling them you will escape trials, tribulations and persecutions, only for eleven out of the twelve to meet a death of martyrdom - that would not have deceived them - instead of them telling to persevere in their faith, even unto death. The early Church fathers knew of persecution of the saints not being the wrath of God, as will the great tribulation, being a trial of faith not to take the mark of the beast, be. The wrath of God will not come on those that by the power of God's Holy Spirit, do not take the mark of the beast during the great tribulation, but the wrath of God will come on those that do.
Daniel 8 (NKJV)
23“And in the latter time of their kingdom,
When the transgressors have reached their fullness,
A king shall arise,
Having fierce features,
Who understands sinister schemes.
24His power shall be mighty, but not by his own power;
He shall destroy fearfully,
And shall prosper and thrive;
He shall destroy the mighty,
and also the holy people.
25“Through his cunning
He shall cause deceit to prosper under his rule;
And he shall exalt himself in his heart.
He shall destroy many in their prosperity.
He shall even rise against the Prince of princes;
But he shall be broken without human means.
26“And the vision of the evenings and mornings
Which was told is true;
Therefore seal up the vision,
For it refers to many days in the future.”