In the days of the apostle Paul, there was “mystery,” or a religious secret, about the identity of this “man of lawlessness.” To this day mystery shrouds his identity in the minds of many persons, because his wickedness is practiced under the guise of godly devotion. (2Th 2:7)

At work in apostles’ days. The apostle Paul said that the mystery was “already at work.” (2Th 2:7) There were those trying to teach false doctrine, some of these even disturbing the Thessalonian congregation, prompting, in part, the writing of his second letter to them. There were antichrists when John wrote his letters, and doubtless before that. John spoke of “the last hour” of the apostolic period, and said: “Just as you have heard that antichrist is coming, even now there have come to be many antichrists . . . They went out from us, but they were not of our sort; for if they had been of our sort, they would have remained with us. But they went out that it might be shown up that not all are of our sort.”​—1Jo 2:18, 19; see ANTICHRIST.