What did Paul mean here then?
"And now you know what is acting as a restraint, so that [the man of lawlessness] will be revealed in his own due time. True, the mystery of this lawlessness is already at work, but only until the one who is right now acting as a restraint is out of the way." - 2 Thess 2:6,7
This is talking about the coming of Jesus. Beginning from the previous chapter to give full context:
We ought always to give thanks to God for you, brethren, as is only fitting, because your faith is greatly enlarged, and the love of each one of you toward one another grows ever greater; 4 therefore, we ourselves speak proudly of you among the churches of God for your perseverance and faith in the midst of all your persecutions and afflictions which you endure. 5 This is a plain indication of God’s righteous judgment so that you will be considered worthy of the kingdom of God, for which indeed you are suffering. 6 For after all it is
only just for God to repay with affliction those who afflict you, 7 and
to give relief to you who are afflicted and to us as well when the Lord Jesus will be revealed from heaven with His mighty angels in flaming fire, 8 dealing out retribution to those who do not know God and to those who do not obey the gospel of our Lord Jesus. 9 These will pay the penalty of eternal destruction, away from the presence of the Lord and from the glory of His power, 10 when He comes to be glorified in His saints on that day, and to be marveled at among all who have believed—for our testimony to you was believed. 11 To this end also we pray for you always, that our God will count you worthy of your calling, and fulfill every desire for goodness and the work of faith with power, 12 so that the name of our Lord Jesus will be glorified in you, and you in Him, according to the grace of our God and
the Lord Jesus Christ.
And moving onto the second chapter:
Now concerning the coming of our Lord Jesus Christ and our being gathered together to him, we ask you, brothers, 2 not to be quickly shaken in mind or alarmed, either by a spirit or a spoken word, or a letter seeming to be from us, to the effect that the day of the Lord has come. 3 Let no one deceive you in any way.
For that day will not come, unless the rebellion comes first, and the man of lawlessness is revealed, the son of destruction, 4 who 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. 5 Do you not remember that when I was still with you I told you these things? 6
And you know what is restraining him now so that he may be revealed in his time. 7 For the mystery of lawlessness is already at work. Only he who now restrains it will do so until he is out of the way. 8 And then the lawless one will be revealed, whom the Lord Jesus will kill with the breath of his mouth and bring to nothing by the appearance of his coming. 9
The coming of the lawless one is by the activity of Satan with all power and false signs and wonders, 10 and with all wicked deception for those who are perishing, because they refused to love the truth and so be saved. 11 Therefore God sends them a strong delusion, so that they may believe what is false, 12
in order that all may be condemned who did not believe the truth but had pleasure in unrighteousness.
So the man of lawlessness is not one who would lead Christians astray (for these Christians abide in the truth with faith and have not been shaken even during times of persecution), but rather, the man of lawlessness is the same as the abomination of desolation mentioned in the Book of Daniel and of Revelation--paganism, hedonism and human pride that leads the nations astray, attempting to usurp God. This was a prediction of the Roman defilement of the Jewish temple, and a warning against the Roman Empire and all worldly kingdoms which set themselves in opposition to God, just as Jesus Himself warned in Matthew 24:15. It was in no way a corruption of the Church, against which the gates of Hades cannot prevail, as Jesus said in Matthew 16.
It was not the Apostles who were restraining the man of lawlessness. Indeed, it is not many people or many things that restrain the man of lawlessness, but one thing or one person. So we know that it was not the Apostles who restrained.
Yes there were Judizers and those teaching that the resurrection had already taken place, but these things were being restrained. The restraining force was of the apostles. Their presence, with their powerful gifts bestowed by holy spirit, prevented apostasy from then becoming an epidemic. (Acts 2:1-4; 1 Corinthians 12:28) But when the apostles had died, by about the end of the first century, the restraining brakes were removed.
It wasn't heresy that was being restrained, but the ragings of the nations, and self-deifying corruptive pride against God.
To put 1 Corinthians 12:28 in its context...
But God has
so composed the body, giving more abundant honor to that
member which lacked, 25 so that there may be no division in the body, but
that the members may have the same care for one another. 26 And if one member suffers, all the members suffer with it; if
one member is honored, all the members rejoice with it.
27 Now you are Christ’s body, and individually members of it. 28 And God has appointed in the church, first apostles, second prophets, third teachers, then miracles, then gifts of healings, helps, administrations,
various kinds of tongues.
Do you believe that no one aside from the Apostles had the gift of the Holy Spirit? Did no other Christian receive instruction in all truth from Him, as Jesus promised in John 16:13? Did only the Apostles receive the graces and gifts of the Holy Spirit to defend the true Faith and to lead and guide the Church? Did no other Christian love the Truth or keep the Faith? Did the Apostles appoint apostates or heretics devoid of the grace of the Spirit to administer the Church? Of course this is not so.
At the end of the century John wrote at Jesus' dictation that there were already sects manifested in the congregations. The sect of Nicolaus, the presence of false prophets like Balaam, and a Jezebel-like influence that called 'herself' a prophetess.—Re 2:6, 14, 15, 20.
There were sects, but they didn't take over the Church. The Apostles and those who they appointed made sure of that, and indeed, we see that the Nicolaitans died out rather quickly.
Once John died, the restraint was gone. False Prophets could take over the administrative nature of the congregations and the real confusion could begin.
So what, you think the Apostles didn't train anyone in the Faith? They didn't have a single thing set in place for after they died? This is, of course, not the case--the Apostles were capable of basic foresight, and had been training and appointing hand-selected successors as bishops to administer the spiritual affairs of the Church.