Adam Clarke

For the mystery of iniquity doth already work - There is a system of corrupt doctrine, which will lead to the general apostasy, already in existence, but it is a mystery; it is as yet hidden; it dare not show itself, because of that which hindereth or withholdeth. But when that which now restraineth shall be taken out of the way, then shall that wicked one be revealed-it will then be manifest who he is, and what he is. See the observations at the end of this chapter (note).