Things the Vow of Poverty does:
- Reassures the citizens of the Empire that the extremely abusable Shadow Magic is in the hands of a group that has strict rules against abusing it.
- Makes it so that if it does appear that someone is abusing it, the first reaction of influential people that hear of it would be to dob them in to the Grey Order, making them able to punish or reassure as appropriate. This makes it so that any negative rumours of Grey Wizards reach the ears of the Grey Order very quickly.
- Gives the Grey Order a way to police its members that does not set uncomfortable precedents for the other Orders.
- Gives the Grey Order a relatively benign pretence to start rooting through any Grey Wizard's affairs, even if they're suspected of something much worse than economic malfeasance.
- Gives the Grey Order a great deal of control over who Grey Wizards end up working for, as anything even slightly amiss can be investigated as potentially running afoul of the Vow.
- Makes Grey Wizards think hard before accepting any job, forcing them at least consider it in terms of what benefit it provides to the Empire, and if there is none, they have to either turn the job down or make it provide some benefit.
- Filters out any potential Wizards who are motivated by a desire for wealth, who might otherwise find the Wind of being extremely sneaky and deceptive very attractive.
- Makes it so the Grey Order, which does not have hugely profitable cash cows like alchemy for the Golds or fortune telling for the Celestials, is able to ensure that its Wizards are properly paying the tithe.
- Puts a test of character in front of all Journeymen Grey Wizards. If they strictly abide by the Vow, then they're suitable for one set of jobs. If they're able to negotiate its loopholes without crossing any lines or raising any stinks, then they're a good fit for a different set of jobs. If they chafe at it and fall to temptation, then better they fall to the temptation of money now than the temptations of the Chaos Gods a decade down the line.
The Vow does seem deceptive, ambiguous, and inconsistent. It's meant to, because that's what Ulgu is. Grey Wizards spend ten years learning how to think like Ulgu before they're let out into the world. Thinking their way through the byzantine snarl of the Vow of Poverty is as natural to them as casting the spells of Shadow Magic.
Things it is not:
- It is not a vow to exist only in a state of poverty.
- It is not a absolutist deontological taboo against ever taking any action that might disadvantage any citizen of the Empire.
- It is not a signed death warrant for every Grey Wizard just in case the Order needs it.
- It is not a vow against exploiting people with magic, only against doing so for the wrong reasons.