"In the name of His infinite wisdom, and by His immortal authority, we, the High Lords of Terra, do hereby decree the Ecclesiarchy forbidden to gather, train, promote, sustain, or in any way command any force of men under arms."
- — The Decree Passive
In essence, it forbid the Ecclesiarchy to "gather, train, promote, sustain or in any way command any force of men under arms," to prevent another occurrence like that of the Reign of Blood in which the High Lord of Terra Goge Vandire became, at the same time, the Master of the Administratum as well as Ecclesiarch of the Adeptus Ministorum, thus making him the most powerful individual in the entire Imperium of Man for a time.
Vandire could keep any Imperial citizen in his thrall with the threat of branding them a Heretic or unleashing the forces of the Ecclesiarchy's Frateris Templars upon any who disobeyed him. This effectively transformed Vandire into the ruler of the Imperium, usurping even the authority of the blessed Emperor of Mankind for the duration of his rule.
The reforming Ecclesiarch Sebastian Thor who replaced Vandire was ordered to carry out this edict, forcing the Ecclesiarchy to disband the Frateris Templar and the armies and fleets maintained by any member of the Ministorum with one exception, the all-female warriors of faith known as the Daughters of the Emperor, due to the infamous loophole in the Decree Passive's wording which clearly specified only "men under arms."
As an all-female militant group, Sebastian Thor argued that the Daughters of the Emperor were not obligated to disband by the Decree Passive, and instead incorporated them into the Ministorum as the Adepta Sororitas, a force that would as much regulate the Ecclesiarchy through their quest for purity as enforce its will upon the faithful.
Goge Vandire, the 361st Master of the Adeptus Administratum, is one of the most reviled human beings in all the history of the Imperium. To his credit, he did manage to break the stranglehold the Ecclesiarchy had over the Imperium's politics in the late 35th Millennium, and engineered the election of an incompetent Ecclesiarch, Paulis III, thanks to contacts he had within the Officio Assassinorum, foremost amongst them the traitorous Tziz Jarek.
Capitalising upon Paulis III's incompetence, Vandire managed to wrest control of the Imperium from the Ecclesiarchy at first, and ultimately installed himself at the head of the Ministorum in Paulis' place after getting rid of the most prominent and troublesome Cardinals.
Vandire, however, soon proved to be even worse: he was a paranoid megalomaniac who believed everyone was out to take his place, and he did not hesitate to use Callidus Assassins to eliminate any individual who dared speak against him, or unleash billions of his faithful Frateris Templar upon any planet who dared to resist him. The Frateris Templar slaughtered millions, even as they fervently believed they were carrying out the Emperor's will. Vandire's exactions lasted for 70 standard years until the reforming priest Sebastian Thor started and successfully led a revolt against the madman.
In the aftermath of the bloody campaigns to retake Terra from the Apostate at the hands of the Adeptus Astartes and the Imperial Guard that led to Vandire's demise, Sebastian Thor, raised in Vandire's place as the new Ecclesiarch, oversaw the implementation of reforms eerily similar to those the Primarch Roboute Guilliman had implemented after the Horus Heresy, to prevent a single individual from ever again gathering enough power through the manipulation of the Imperial Cult to threaten the stability of the Imperium.
Amongst the many reforms were the creation of the Inquisition's Ordo Hereticus and the Ordo Sicarius, intended to maintain a watch over both the high officials of the Imperium and the Officio Assassinorum. But most central to the reforms of Sebastian Thor was the Decree Passive, which forbid any member of the Ecclesiarchy, under threat of execution, to retain any "men-at-arms" under his or her control.
However, the Orders Militant of the Adepta Sororitas remain exempt from the Decree Passive ostensibly because they are made up entirely of female warriors, but also because Sebastian Thor understood that the Ecclesiarchy could not sustain itself without some form of armed protection.
He thus expanded the organisation of the "Daughters of the Emperor" who had proven their steadfastness and unshakable loyalty to the Emperor during the Reign of Blood into the Adepta Sororitas, and allowed the creation of their Orders Militant, the many different orders of the Sisters of Battle.
However, the Adepta Sororitas also serve as the Chamber Militant of the Ordo Hereticus; should any member of the Ecclesiarchy again see to thwart the will of the Emperor, the Sisters of Battle will be the first to stand against them.
In the late 41st Millennium, the Decree Passive is still enforced, but less zealously; bands of Frateris Militia are allowed to gather in the shrines and holy places of the Ecclesiarchy, and crusades of the wild-eyed religious zealots such as the Redemptionists have been tolerated, albeit under strict monitoring by the Ordo Hereticus.
Cardinals and high ranking Ecclesiarchy priests are still not allowed more than a few Crusader bodyguards in day-to-day life, however the Decree Passive can be circumvented when tidings are dire for the Imperium by having an official of the Departmento Munitorum rubber-stamp an approval to conscript the Frateris Militia as Imperial Guard auxiliaries for the duration of an emergency, allowing the Ecclesiarchy to equip and lead the faithful without the risk of being executed even if they prove victorious.
- Codex: Assassins (2nd Edition), pp. 3-5
- Codex: Sisters of Battle (2nd Edition), pg. 16
- Warhammer 40,000: Rulebook (4th Edition)
- Wrath & Glory: Rulebook (RPG) (Cubicle 7 Revised Edition 2020), pg. 50
- Legion of the Damned (Novel) by Rob Sanders