The Order of Planes militant (aka: The Children of Heaven, the Brethren, the Faithful)

Sect History
The Brethren are an old and venerable sect. Close to two-thousand years ago, the son of a solar archon, who had journeyed the planes spreading the word of lawful goodness, appointed one man to be the leader of his righteous cause when he was gone. This chosen man's name was Pitre Prefectii. Under him, the followers of the solar's son united and formed the sect known as the Brethren. They unanimously recognised Pitre as their leader, as he had been the chosen one, and they gave him the title Chosen.
For the first couple of centuries, the Brethren were acknowledged as little more than a cult. Occasionally, a Brother would leave the safety of Mount Celestia to spread the word of The One. Unfortunately, these messengers were little more then annoying preachers in the Upper Planes, dissenters in the Lawful Planes, and breakfast in the Lower Planes. It wasn't until the Brethren were acknowledged by the archons of Mount Celestia as a sect that the tiny group was able to establish itself as a planar power.
Following their formal recognition by the archons, the Brethren underwent a period of magnificent rebirth, in which they reorganised their ranks, established strongholds and updated their doctrine. During a five-year convention, called the Reformative Council, the Brethren established titles, ranks and laws by which the sect would function by. The leader of the Brethren, it was decided, would be voted into office via a blind ballot, following a series of verbal, mental and physical tests. This leader would be called a Prefect, in reverence of the first sect leader, Pitre Prefectii. In a remarkable leap of faith, the archons assigned one of their own to be the advisor to this Prefect, and by doing so the alliance between the Brethren and the natives of Mount Celestia was formed.
During the Council, policies were formed regarding the sect philosophy. Some of the Brethren wanted to update the ideals of the sect, shifting the focus from the Chosen One to the overall spread of good. The more conservative Brethren argued that, had it not been for the Chosen One, the sect would never have come into existence in the first place, and therefore the ideology of the Brethren should stay focused around the Chosen One's teachings. A long debate ensued, in which it was finally decided that the Chosen One's teachings would be the basic tenets of the Brethren's philosophy, but that the Brethren would not continue to base itself around the Chosen One.
After the Reformative Council, the Brethren (who still had not adopted the name we know them by now) experienced another period of rebirth, in which membership expanded geometrically. Residents of the gate-towns that linked Mount Celestia to the Outlands joined in large numbers. Sometimes entire towns would sign themselves over to the Brethren, and it is these towns that are, even today, the strongholds of the sect. Petitioners of the Mount who had not been worthy enough to become archons signed on en masse.
Then disaster struck. In a surprise attack against the Mount, an army of baatezu laid siege to the first layer of the plane, destroying dozens of towns and numerous Brethren monasteries before they were finally beaten back by the archons. Hundreds of Brethren had been slaughtered in the attack, and this taught the growing sect a powerful lesson: sometimes one must fight for what one believes in.
Another convention was called, this one decidedly shorter then the previous one. Called the Defensive Council, the attendants of this convention decided overwhelmingly that a more militaristic stance must be taken by the Brethren -- in the name of good, of course. Changing their sect's name to the Order of the Planes-Militant, the Council appointed two new titles to the Order's ranks: Marshal and Watchman. Now, the Order would not just preach goodness, but defend the innocent and fight evil where ever it was found.
And so it has been to this day. The Order has gradually grown more and more militaristic over the centuries, but they still maintain their doctrine of conversion. Brethren can be found throughout the Upper Planes of Bytopia and Elysium, preaching the benefits of lawful goodness and structured utopia. And while the preachers and converters of the sect work the Upper Planes for possible members, the Faithful's warriors charge into the Lower Planes and the Outlands, combating evil and defending the weak.

Sect Headquarters
Mount Celestia, the structured utopia, the ordered paradise. Here, among the archons, the Faithful make their home. On the fourth layer of Paradise, known as the Electrum Heaven, the Brethren's headquarters can be found. The First Monastery of the Planes-Militant is a gothic-style complex built atop a rocky plateau just above the clouds. The First Monastery was built to be totally self-sufficient. And it is. The building contains dozens of granaries, hundreds of water reservoirs, innumerable stables and feeding pens for a million animals. There are enough bedrooms for half a million Brethren, enough training rooms for fifty armies, and more then enough kitchens to feed both.

Membership
The Faithful aren't picky about race or gender, but a cutter has to be lawful good. Chaotic and neutral berks can't stand the restricting oaths they have to swear, nor do they like the limiting policies of the Faithful. Evil cutters loath the idea of sacrificing of themselves to help others. So, it's not that the Brethren only allow lawful good members, just berks who aren't lawful good simply don't want to join.
Once someone signs up for the Order, they are subject to a two-week long observation period in which they are monitored by the local Watchman. If the subject is considered "good" enough by the Watchman, he may take an Oath of Fealty to the local Marshal. Once this has occurred, the subject is considered a Lay-Brother or Lay-Sister. From there, through good deeds and outstanding service to the Faithful, the person may be promoted to higher ranks. A great majority of Faithful remain Lay-Persons all their life, however.

Structure
At the very pinnacle of the Order is the Prefect, as mentioned previously. The Prefect is generally considered the smartest, strongest and most able leader of the Faithful can provide, and the Brethren base their spiritual and physical strength by the strength of their Prefect. If a Prefect is a dull, weak leader, then the Order must be dull and weak, and needs revitalisation. If a Prefect is charismatic, powerful and intelligent, then the Order is strong. Since the near-beginning of the sect, the Prefect has been attended to by a planetar advisor.
Beneath the Prefect is the Metropolitan, who is the religious leader of the sect. The Metropolitan is responsible for the spiritual well-being of all Faithful, and ensures both loyalty and purity of heart in the Order's members. Throughout the centuries, the Metropolitan's station has varied in importance and prominence. Some Metropolitans have been inquisitors, rooting out "evil" and "corruption" among the Brethren through elaborate trials and tortures. Some Metropolitans have been obscure clerics who stand idly by while fiends corrupt the sect's members. The current Metropolitan is Purity III, a cleric who has made a name for himself as an easily accessible listener and healer.
Equal to the Metropolitan in status is the Keeper of the Seals, who serves as an advisor to the Prefect. It is the Keeper of the Seal's duty to not only counsel the Prefect, but to also monitor His (or Her) Holiness for signs of corruption. The Keeper is typically a very powerful mage, and the current Keeper lives up to that stereotype. Indigo the Stutterer, an extremely potent mage, holds this position.
After the Keeper and Metropolitan are the Marshals, who serve as the generals and high-ranking military leaders of the Brethren. Marshals are responsible for leading forays into the other planes, fighting evil and chaos, and establishing outposts for the Order.
Housewardens are the individual leaders of the Order's outposts. Their duties include defending the Order's strongholds, serving as officers in a Marshal's army, or acting as aides to higher-ranking officials. A Housewarden is typically the highest ranking Brethren in any given stronghold.
Serving the Housewardens are captains and lieutenant, the Watchmen is often given units of Crusaders or Lay-Brethren to lead. A Watchman's duty may include leading a patrol, acting as a captain of the guard at a Brethren stronghold, or serving as bodyguard to a Marshal or Housewarden.
The Crusaders are the footsoldiers of the Order, acting as warriors, scouts, preachers, researchers and the like. A Crusader reports to his assigned Watchman on a regular basis.
Finally, the bottom rung of the Order are the Lay-Brethren, who are ordinary men and women who are responsible for the day-to-day operations of a Brethren outpost. It is the Lay-Brethren who feed the horses, clean the stables, cook the food, and maintain the weaponry and armour of the Order. Although regulated to menial tasks, the Lay-Brethren bear their duties with good cheer and a smile, knowing that all Faithful started out where they did -- even the Prefect herself.

Allies & Enemies
The Faithful get along great with good-aligned groups, such as the Harmonium, and good-aligned races like the aasimon. The Order has a friendly neutrality towards the Fraternity of Order, and tries to ignore the goings-on of the Mercykillers. Although the Faithful do not agree with the tactics of the Red Death, they realise that the faction gets the job done.
The Brethren loath such groups as the Athar, the Bleak Cabal and the Doomguard. They work tirelessly to expose the false beliefs of the first faction, and combat the later two wherever they can be found. The Order's primary foe, however, are the fiends of the Lower Planes, and they consider it their primary goal defeat the evil monsters.

Advantages & Disadvantages
Brethren are always able to seek succour from fellow Brethren. If another member of the Order appears in your doorstep, it is your duty to take him in, feed him, tend to his wounds and help him in any way possible. To turn away a fellow Faithful is dishonourable and evil, and to do so is an excellent way to be removed from the Order.
In return, the Order requests that all members swear oaths of fealty, chastity and poverty, similar to the oaths sworn by paladins. A member of the Order may never disobey a superior, no matter what. Unless the mission assigned to you is obviously evil or chaotic, you must complete it. In the event that an order is in someway evil, a Brethren must report this to his superior's superior. Also, a Faithful may only keep as much jink as he needs to maintain a moderate standard of living, as well as other necessities, such as a horse, armour, weaponry, etc. The rest should be donated to some worthy cause (although preferably to the Order).