For the mystery of lawlessness already works. Only there is one who restrains now, until he is taken out of the way.
The restraint - 1) If the "man of sin" was Jewish, and their persecution of Christians, it is the Roman government that serves as the restraint until the rebellion AD 60-70. Matthew 24:22; 1 Peter 4:17-18. 2) If the "man of sin" was Nero, and his persecution of the Christians, the restrainer was someone else. 3) Some maintain that the Latin name of Claudius, the contemporary Emperor, was related to a Latin word "restrain". [IVP Bible Background Commentary, p. 601 Rt Bm)