In the Word of God we see two great mysteries, which develop themselves during the present dispensation: the mystery of Christ and the mystery of lawlessness. The counsels of God engaged in the first have their accomplishment in heaven. The union of the body of Christ with Himself in glory will evidently have its accomplishment there on high. But, by the power of the Holy Spirit, there ought to be on earth during this dispensation the manifestation of the union of the body of Christ. But here the responsibility of man comes in for its share in this manifestation here below, although in the end all will be to the glory of God. Therefore the dispensation may be in a state of ruin, although the counsels of God never fail; on the contrary, our lie will turn to His glory, although He judges righteously.
In this sphere of man’s responsibility, Satan can introduce himself the moment that man fails to lean absolutely upon God. We know this by every day’s experience.
The Mystery of Lawlessness
It is then revealed that the mystery of lawlessness will have its course. Here it is not a question of counsels, but of an evil done in time. The question here is of this mystery of lawlessness; the apostasy or falling away is not a mystery. There is no need of a revelation to inform us that a man who denies Jesus Christ is not a Christian; he says it. But in this case, it is an evil that has commenced working in the bosom of Christendom, in relation with Christianity — a mystery of which the lawless one will be the full revelation, as the glory of Christ and of the church will be the full accomplishment of the mystery of Jesus Christ. The words translated in most versions “iniquity” and “wicked one” are the same in the original, save that one indicates the thing and the other the person. It is “lawlessness” and the “lawless one” preeminently. This mystery of lawlessness commenced working in the Apostle’s time; later the veil would be removed. The apostasy would be then, and at length the lawless one would come to his end by the appearing of the coming of Christ. Thus is the dispensation to be brought to an end: This is what we have revealed in this passage. Hence, as we see elsewhere, this will be to introduce the glory and reign of Christ, so that all the earth may be filled with the knowledge of the glory of God.
Collected Writings of J. N. Darby, 1:175