My first ending in Dark Souls 3 was the Linking the Fire ending, where your character follows the age-old duty of immolating their soul(s?) in order to feed the First Flame that Lord Gwyn sacrificed everything to prolong. However, in stark contrast to the fiery explosion that engulfs the entire Kiln in Dark Souls 1, the First Flame in Dark Souls 3 languidly licks its way around the character’s silhouette. This ending was initially unsatisfying for me, as both a direct repetition of the endings of Dark Souls 1 and a weak climax. However, I now feel like this detail helps demonstrate the passage of time better than most of the rest of the game, but it also leans on some of the other information provided by other world details. The Deep and the Profaned Flame are both areas of the Dark Souls 3 lore that are largely left vague, but both could be linked to the Abyss, Humanity, and the waning power of the First Flame.
In the Cathedral of the Deep, deacons who likely once revered the Gods such as Gwyn, and helped to serve the Flame and Gwyn’s legacy by offering Humanity to the bonfires (source: Archdeacon set, Way of White covenant in Dark Souls 1), have since fallen to the influence of other powers, such as the Deep, Pontiff Sulyvahn’s Profaned Flame, and Rosaria. If one is to accept the theory that the Human Dregs item from the Aldrich Faithful covenant are a form of Humanity which has become corrupt by the influence of the Deep, then even the Humanity which the Way of White once sacrificed to the Gods is being influenced by the mysterious Deep. Water was previously used in Lordran in an attempt to counteract the Abyss when the Four Kings of New Londo fell to its influence (source: New Londo Ruins), but perhaps water has/had other interactions with the nature of Humanity and the Abyss that have rendered some Humanity unable to be used in the Rite of Kindling.
The Profaned Flame is a new player on the stage of Dark Souls lore that is also related to the Cathedral of the Deep and Way of White. Due to the involvement of a former Way of White deacon (Archdeacon McDonnell), speculation can be made about the possibility of Humanity being burnt to feed the Profaned Flame as well, drawing even more power away from the First Flame. In addition, Archdeacon Klimt and his followers also abandoned the Way of White, instead choosing to commit to a theology similar to the Darkwraiths but focused on the harvesting of other ritualistic sacrifices, namely tongues, for Rosaria.
All of these details about the Cathedral of the Deep indicate at least one thing: the Way of White and the tradition of sacrificing Humanity to further extend Lord Gwyn’s Age of Light has largely been abandoned by the world at the time of Dark Souls 3. Even Prince Lothric, the character that was supposed to be next in line to become a Lord of Cinder, has been dissuaded away from linking the fire. If you choose this ending, your character is choosing to uphold the expectations of the Lords of Cinder and Way of White, and supporting Lord Gwyn’s legacy by extension, but the result is simply far less spectacular than in the days more closely following Gwyn’s reign. The tradition has fallen out of favor with the majority of the world’s population, either by choice, demand, circumstance, or something in between. Perhaps the Profaned Flame is part of, or created from part of, the First Flame, ensuring that an ember of the First Flame will persist in the Age of Dark, as has long been foretold. However, the Age of Gwyn’s Light, for which he kindled the First Flame with his own Lord Soul, is drawing to a definite close in Dark Souls 3.