The falling away, or apostasy, is an aggressive and climatic revolt against God which will prepare the way for the appearance of the man of sin (see I Timothy 4:1-5; II Timothy 3:1-5). The man of sin is literally the man of lawlessness. While it is true that the forces of lawlessness were at work in Pauls time and are at work today, the man of lawlessness is an individual of the future who will come to power during the Tribulation days.
The antichrist is currently being held back by a restrainer. Some understand this to be God indwelling His Church by the Holy Spirit, while others see human government as the restraint. According to the former view, the removal will be at the rapture of the church, according to the latter, it will happen at the overthrow of human government at the hands of the antichrist.
Pauls argument in II Thessalonians can be summed up as follows. [1] The day of the Lord will not begin until the antichrist is revealed. [2] The antichrist cannot begin to act until the restrainer, the Church or believers, are removed. [3] Since the restrainer has not been removed, the Day of the Lord cannot have begun.
It is evident from John 16:7,8 that the work of the Spirit in the world is that of conviction and restraint concerning sin. He accomplishes this work through the bodies of those He indwells (I Corinthians 6:19). Spirit-indwelled believers have a purifying effect on the world. The Antichrist cannot be revealed until the Bride of Christ (the Church all believers dead and living) are removed (II Thessalonians 2:3,7,8).
This does not mean that the Holy Spirit must be removed from the earth. This is not possible since He, as God, is omnipresent (present everywhere at all times) Psalms 139:7-11 and always will be.