Matthew Poole and continuators on 2 Thessalonians 2:7

7 For the mystery of iniquity doth already work , only he who now letteth will let until he be taken out of the way .

The way was prepared by degrees for the man of sin, before he came actually to be revealed, or constituted in his compleat existence. And this was by the working of the mystery of iniquity. A mystery is something in general which is abstruse, intricate, and not easily discerned. And there are mysteries in Doctrine, and in Practise; and there are mysteries of Godliness, and mysteries of iniquity, mysteries of the Kingdom of God, and the Devils Kingdoms. So there are the deep things of God, 1 Cor. 2.10. and the depths of Satan, Rev. 2.24. the mystery ushering in the man of sin is a mystery of iniquity. It is not open sin and wickedness; but dissembled piety, specious errors, wickedness under a form of Godliness cunningly managed that is here meant. See the Book called the mystery of Jesuitisme, or the Provincial Letters. And it is a mystery that worketh; it doth exert and put forth it self, but secretly, as a Mole which worketh under ground. And its working is not against the Being, Providence, and Attributes of God, or natural Religion; but to undermine Christianity in the peculiar Doctrines, Worship, and Practise of it. In Doctrines, are brought in privily damnable Heresies, 2. Pet. 2.1. In Worship, inventions and commandements of men, under pretences of greater reverence, devotion and humility, Col. 2.23. In practise, dispensations to moral impieties under colour of service to the Catholick Church. And this mystery, saith our Apostle, already worketh: in the false Doctrines of the false Teachers of his time, in the Traditions, and Inventions of men obtruding themselves into the Worship of God in his time, in the affectation of pre-eminence in the Church in his time, and making merchandise of the Gospel in his time, and gain Godliness: And in mingling Philosophical notions with the simplicity of the Gospel, and gratifying the flesh under a form of Godliness, and pretence of Gospel liberty. And it was not among the Heathen, or the Jews, but among the professours of Christianity that this mystery was then working, as I suppose the Apostle meaneth. And when the man of sin was fully revealed all these corruptions did centre in him, as sinks in the common shore: the lesser Antichrists in the great Antichrist.

The Idolatries and Persecutions of the Heathen Emperours must be taken out of the way to make way for those that arise under a Christian or rather Anti-christian State, the Dragon giving his Seat, Spirit, and Power to the Beast. And the Power that was in the Roman Emperour whether Heathen or Christian must be taken out of the way to make room for the Exaltation of this man of Sin. For notwithstanding all corruptions in Doctrine, Worship or Practise which might be introduced before, yet he is not fully revealed till he hath his jurisdiction and secular power also in his hand. And then this mystery of iniquity is arrived to its height; which St. Iohn saw written in the forehead of the great Whore, Rev. 17.5. Mystery, Babylon the great &c. and which some have said, was written anciently in the Popes Mitre.