Shared ground
Paul treats the Thessalonians’ confusion as a memory problem, not a lack of access. He says he already spoke about “these things” when he was with them (explicit claim). The letter assumes earlier face-to-face teaching is a reliable reference point (inference from v. 5).
Paul also presents the present moment as controlled: something is restraining “him” so that he will only be revealed at the right time (explicit claim). At the same time, “lawlessness” is already active in a hidden way, yet checked by a restraining reality “now” (explicit claim). This creates a two-level picture: present hidden activity and present restraint.
Where interpretation differs (only where needed)
What is the restraint / restrainer? Paul says they “know” it, but he does not name it here (explicit). Interpreters therefore differ on what best fits the letter and the wider setting (inference). Some argue it is a personal agent (“the one who restrains now”) acting with purpose; others think Paul is describing the same restraining reality two ways—first as a thing (“what restrains”) and then as a person-like description.
What does “taken out of the way” mean? The text states that the restraining influence lasts “until” the restrainer is “taken out of the way” (explicit). Some read this as full removal; others as being moved aside so it no longer blocks; others as a loss of restraining power without implying disappearance.
Why the disagreement exists
Paul uses both a “what” and a “who” description, but gives no identifier in these verses, and he leans on shared prior teaching (“you know”). Also, “mystery of lawlessness” can mean “hidden/undercover operation” or “not fully disclosed yet,” and both sense options affect how one pictures the present and the future sequence.
What this passage clearly contributes
These verses add the idea of present restraint alongside present hidden lawlessness: the final open “revealing” is delayed, not absent. They also show Paul’s expectation that apostolic teaching included details not repeated in the letter, so the community’s understanding depends partly on remembered instruction, not only written text. Finally, the timing (“in his own season”) implies an ordered sequence leading into what Paul will describe next (see 2 Thessalonians 2:8).