Who is this one who reatrains the anti-Christ or "man-of-sin" in the days of Paul?
And now ye know what withholdeth that he might be revealed in his time. For the mystery of iniquity doth already work: only he who now letteth will let, until he be taken out of the way. 2 Thessalonians 2:6,7
1) He had already told them who it was- Remember ye not, that, when I was yet with you, I told you these things? 2 Thessalonians 2:5
2) They knew what it was- And now ye know what withholdeth that he might be revealed in his time. 2 Thessalonians 2:6
3) But there was some reason Paul didn't put it in writing.......
Early Church fathers such as Tertullian, Jerome, Augustine, Chrysostom & Irenaeus all told us it was the power of the Roman Empire.
This would make sense. Also, since the Little Horn of Daniel is seen to be the anti-Christ, (Papal Rome), he didn't rise until after the fall of the Roman Empire, when there was no one to restrain his lust for power.
Remember this "man-of-sin"/anti-Christ/Little Horn of Daniel/ Beast of Revelation power , once unleashed, would last until the end of time- And then shall that Wicked be revealed, whom the Lord shall consume with the spirit of his mouth, and shall destroy with the brightness of his coming: 2 Thessalonians 2:8