I had my own theory about this way before it was announced but after seeing some spoilers and not being to thrilled with the end result i would like to share what i thought would happend and why it makes sens to me.
Imagen while working for your covenant you are tasted in dealing with a creature that is causing havok, world boss, raid, torghast dont really mader, after beating it in to submission beacuse thats how we deal with most the problems.
The covenant trys to process the soul in their own way, taxing and near impossible as the soul is violent, strong and lashes out allot, but through hard work and exposing it to new things other then they pain and rage it felt it starts to gain an understanding.
knowing not who or what it is by the end of your campain it decideds it wishes to explore more of the other covenants and learn other virtues and experience more emotions.
From a lore standpoint the soul now travles between covenants and meets other champions, from game standpoint you as a player kickstarted this process.
This soul would have been none other then Argus, while it would not have been an easy feat to pry the jailor of this priced soul it’s hardly like we where not already treating his jail tower as an anima supermarket.
Having been deprived of a proper life himself he would not only find a worthy purpes but also experience life, al it’s joys and sorrows through the eyes of others, with a understanding of the afterlifes he guides them to,
A tale of rising above your pain and becoming something possetive is always a compelling tale to me, naturaly this is my opinion and everyone is free to tell me how wrong and stupid i am