Adam Clarke on 2 Thessalonians 2:5

I told you these things - In several parts of this description of the man of sin, the apostle alludes to a conversation which had taken place between him and the members of this Church when he was at Thessalonica; and this one circumstance will account for much of the obscurity that is in these verses. Besides, the apostle appears to speak with great caution, and does not at all wish to publish what he had communicated to them; the hints which he drops were sufficient to call the whole to their remembrance.