The Apostle Paul
2 Thessalonians 2:7BSB·traditional attribution

For the mystery of lawlessness is already at work, but the one who now restrains it will continue until he is taken out of the way.

John Calvin Reformed @genevareformer

7. The mystery of iniquity. This is opposed to revelation; for as Satan had not yet gathered so much strength, as that Antichrist could openly oppress the Church, he says that he is carrying on secretly and clandestinely “Et comme par dessous terre;” — “And as it were under ground.” what he would do openly in his own time.

Matthew Henry Presbyterian @wholebiblehenry

In these words the apostle confutes the error against which he had cautioned them, and gives the reasons why they should not expect the coming of Christ as just at hand. There were several events previous to the second coming of Christ; in particular, he tells them there would be, I. A general apostasy, there would come a falling away first, Th2 2:3.

Commenting on 2 Thessalonians 2:3-12

John Gill Reformed Baptist @doctorgill

For the mystery of iniquity doth already work,.... Or "the mystery of that wicked one", as the Syriac; meaning either antichrist himself, and the spirit of antichrist, which were already in the world, Jo1 2:18, "mystery" being one of the names of antichrist, Rev 17:5 and anciently this word was engraven on the mitres of the popes of Rome: or the evil doctrines and practices...