Sartur is an ancient deity, once the enemy of the Northern Gods. Now many have flocked to his worship to escape the predations of the Zells.
Sartur's teachings explain that the reason why some parts of the world are more rich, more fertile and generally better than the others is because there is a finite amount of blood in the cosmos.
And those sons of bitches, those guys living in cities, and dense towns with millions of people? Yeah, they're hording all of the blood. The fuckers. They're hording all of YOUR blood.
"But that's not fair!" you cry, your belly empty and your children hungry from the wasted harvest.
Well don't worry. Sartur has your back. See, if you SPILL the blood, then it goes into the ground. And Sartur is of the ground. And he will redistribute the blood to people who deserve it.
So you just need to spill blood for the blood god, and your lands will improve.
Sarturi are in general hateful of Genosians, who hunt Sarturi as well as living in cities. They also see the Karthacki as a major part of the problem.
The Sarturi tend to get along best with the elves of the forests. Since Ohanedin don't exactly live in big cities, and obviously aren't part of the "problem" that Sartur is trying to deal with, generally they don't get in a big huff over it unless they were already pissed off over something else.
The Chosen of Sartur are Ascendant humans, charged with killing lots of people and shedding lots of blood. They can use the blood they spill to make themselves huge and powerful, or dedicate it to the land making it incredibly fertile.
Most of the Chosen aren't Sarturi. They don't even know who Sartur is. They are people who embody his virtues. They are people who thirst for something so greatly that they would drink a river of blood for a thimble full of vindication.
If you have ever hated enough to impale ten thousand people on stakes, you could be a Sarturi.
If you have ever hated enough to destroy a city and everything in it, including its books, its wisdom, its history and its art, you could be a Sarturi.
If you have ever hated enough that you would have eighteen thousand mens' eyes gouged out to prove a point, you could be a Sarturi.
If you live comfortably and well and want for nothing, but still want to see society collapse so that others will suffer for their hedonism, you could be a Sarturi.
If you would burn the world clean of all life just to be sure you killed one specific person on it, you could be a Sarturi.
These people emerge not because of what they have done, but because of what they may yet do. Sartur is unique in that he knows men not by their actions, but by their hearts.