“And now ye know what withholdeth that he might be revealed in his time.”
King James Version (KJV)
2:6 And now ye know - By what I told you when I was with you. That which restraineth - The power of the Roman emperors. When this is taken away, the wicked one will be revealed. In his time - His appointed season, and not before.
2Th 2:6 Now ye know what withholdeth that he might be revealed in his time. They knew because Paul had told them when with them. We have not that advantage, but I believe that he told them that this development could not take place until pagan imperial Rome fell. We know that it did "withhold", or prevent it.