When Paul, in his second letter to the Thessalonians, warned the congregation of this coming “man of lawlessness,” the details of that one’s lawless course were still a “mystery,” or a religious secret. However, the apostle mentions that even while he was yet with them he “used to tell” of this future apostasy and the “restraint” holding it back.​—2 Thessalonians 2:5-7.

Such elements of counterfeit Christianity were already “at work” among professing Christians in Paul’s day.​—1 Thessalonians 4:3-8; 5:6-9, 14, 15, 19-22; 2 Thessalonians 3:6-15; compare Matthew 25:41-46.

Paul and the other apostles and older men of the Christian congregation served as the “restraint” against such forces, shepherding the flock according to Christ’s example.