I read fpruller's great article about Rondra, and thought instead of commenting I might write this instead.
The world of The Dark Eye, Aventuria, has existed and got changed since the 80ies. Very early on the Twelve gods of the main human Pantheon were named and established. In countless adventures over the years, adventures have noticed the influence of the gods, learned of their histories. But with the current edition of the rules, the world background has begun to change.
The Starfall was an unmissable sign that the current age is ending, and soon a new age will begin. As it says in the Aventuria Alamanc: One constellation, the Hero, shines brighter than ever before in the skies over Aventuria, and for the first time in living memory, humans and dwarves can agree on this at least—the continent is experiencing a new Heroic Age.
This heroic age, in which the adventures and stories of The Dark Eye are set, is a time of change, not only for Aventuria, but also its gods. One of the potential changes is Rondra. The worship of Rondra is often seen as idealistic. Back, in the good old days, noble knights might meet on the field of battle, and so a few well-trained and well-equipped warriors could determine the outcome of a large conflict.
In recent years many parts of the realm have seen bloody civil war, invasions of otherworldly forces and other traumatic events that make people question whether battle or war is not fundamentally different, from Rondra's lofty ideals. Maybe it is fine to have honour if from a young age you were trained in the art of fighting, have the best armour, and a blade blessed by the heavenly lioness. If, on the other hand, you are poor, poorly trained and fighting for the survival of your family, surely you will take every single advantage you can get, honourable or not. This is, where in the first instance, Rondra's own son, Kor comes in. Myth has it that Kor is the son of Rondra and the great dragon Famerlor. Famerlor is said to be the defender of the gate to Alveran, where the gods dwell. Unlike his mother, Rondra, Kor is a god of mercenaries, gladiators and everyone who fights for a living. Often described as "The Merciless", Kor wants his followers to win first, and worry about what they had to do to achieve it, later. As a god of mercenaries he values agreements and his holy texts lay out the relationship between those who hire the warriors and the mercenaries themselves. These texts also define the mercenary's honour (work against those who defile people or things), but also the rewards the mercenaries can expect for their willingness to risk their live (plunder and the like). So maybe Kor might be more suited to become the god of war in Aventuria, and ultimately, when this heroic age ends, sit in Alveran? Maybe there are other, less remembered gods which might wish to lay a claim. But don't ever count out Rondra, after all when things look the most bleak, then it is time for true heroes to shine. For ages philosophers in Aventuria have, behind closed doors, discussed just how much the gods shape the people in Aventuria, through their laws and judgements and how much the worshippers might shape their gods. But for us players and game runners alike, this conflict around the churches of Rondra can be seen in a number of the published adventures and stories. Especially Arivor's Doom and the Theatreknight campaign allow the heroes to not only experience the changes in play, but maybe even to influence both national politics and through that maybe even larger changes behind the scenes. Now, looking a little at the future. What the official canon will be, only the good folks from Ulisses can say, but how interesting would be it be if Rondra lost her seat in Alveran, say Kor had become the new god of battle and war. What changes might that bring to the realms in Aventuria. How many blessed ones might convert to her son? Would the worship of Rondra become outlawed in places, as she no longer is one of the twelve? How interesting would the underground secret church of Rondra suddenly become. Relics, clinging to the old ways in a world which has little need or room for honour?
That is part of the beauty of playing The Dark Eye. My Aventuria, shaped by choices and events my players were involved in, can look very different from your Aventuria. So it will be interesting to see how the perception of the Rondrian church will fare in the Bornland and elsewhere whilst my players walk in the footsteps of the original Theatreknights. My own group is currently about two thirds through Arivor's Doom, and I believe after that they will head pretty much straight to the Bornland what awaits them there remains to be seen.
As always if you want to read up on things to do in The Dark Eye, start in the Aventuria Almanac. If you want to play either a blessed one of Kor or Rondra, you should look into the Gods of Aventuria for all their gifts and powers and the like. But seeing that this is so important to the background of the Theaterknight campaign Ulisses translated the Kor Vademecum, an in world text of the faithful, discussing their faith. You can get it on DriveThroughRPG here: https://www.drivethrurpg.com/product/330632/KorVademecum-PDF
This book gives tons of in game lore and perspective. You can easily take buckets of prayers and the like to give flavour to NPCs or your own character. Also, I love the pencil art in it.