"Blessed are the righteous, the lights in the shadow
In their blood the Maker's will is written."
Canticle of Benedictions 4:10-11
Here's a pattern I noticed regarding how blood and songs are used to control people in Dragon Age.
First, let's examine blood magic, i.e. the type of magic that's infamous for being capable of mind-control and something Tevinter seems to especially love. The same Tevinter that copies everything the ancient elves have ever done. The Scrolls of Banastor has this to say about blood magic:
"To align with the power of the Fade is but the first of many steps. Further is to align the mind to the Fade's rules and find the ties between the realm of the dream and the realm of the flesh. This is the true power of blood magic: the flesh and the mind are inseparable, and therein lies the power to influence and control minds."
Codex entry: Scrolls of Banastor
Meanwhile, Avernus says this:
"Our power attracts [demons and spirits], and for a good reason: our unique bridge between flesh and dream is one way they can enter the realm of the flesh."
And one last codex entry from Awakening:
Studies of the Veil have never been thorough. The Tevinters once theorized that the Veil is thin in places that have seen great bloodshed. As the Chantry is so fond of reminding us, the magisters of the Imperium only once crossed physically into the Fade, the catastrophe that blackened the Golden City. As the story goes, the ritual consumed a vast quantity of lyrium and the blood of a hundred slaves. But was it the deaths that bridged the worlds, or simply the blood and lyrium? Or both?
Demons seize every opportunity, every tear in the Veil, to enter our world. Once the Veil is torn, it is extremely difficult to mend, some say impossible.
Codex entry: Tears in the Veil
If blood is some kind of doorway between the Fade and the physical world, it can serve as an entry point for spirits and demons who want to experience the physical world. But here is the thing: a door can be opened from both sides. If blood opens a way for spirits and demons from one side, then it opens a way for humans and other physical beings from the other side too, making it possible for them to physically enter the Fade. No wonder Corypheus and the Magister Sidereal sacrificed so many slaves to breach the Veil and enter the Fade.
Blood serving as a gateway between the Fade and the "realm of the flesh" basically means it enables possession and control which would explain why spirits and demons are particularly drawn to blood mages. But all mages can become targets as we've seen with Wynne, Anders, Connor, and Flemeth who are all variations on the same theme:
Wynne was possessed by a spirit of Faith and the two of them managed to work together more or less effectively.
Connor's actions in DAO make it pretty clear he never had any control over the demon that possessed him in the first place.
Anders was also willingly possessed by a spirit (Justice) who was eventually corrupted by Anders's anger and became a demon (Vengeance), making Anders struggle to maintain control throughout most of DA2. In Act 3, he even claims that he and Vengeance are now "one".
Flemeth is an interesting case. She has this to say about Mythal:
"She is a part of me, no more separate than your heart from your chest."
This sounds like Anders, except less volatile, which is weird because Flemythal's character also revolves around taking revenge for the injustice that has been done to her. One of her titles is "Mother of Vengeance" of all things. Flemeth agreed to become the host of Mythal because both of them wanted vengeance, while Anders agreed to become the host of Justice because both of them wanted justice. The host very clearly has to agree with the possession to work, though as we've seen with Connor, the host can agree out of desperation/ignorance/etc and end up doing things they would regret. This is also why Flemeth telling Morrigan "a soul is not forced upon the unwilling" is true but also suspect: demons trick their desperate hosts into an agreement all the time (see also the "choice spirit" Imshael). Her intended gift in DAO to Morrigan was called Robes of Possession and it came with -1 Willpower and the following description:
"The original intent of these robes is clear: a "welcome home" present from Flemeth, designed to sap Morrigan's will and ease the ancient sorceress's possession of her daughter."
All of the above is also why I think necromancy and mind-control through blood magic are basically just possession-lite. The mage's soul (probably) doesn't literally enter the other person's body/corpse but they can puppet them around.
Speaking of possession, we also have a Tevinter Magister dabbling in controlling others through blood: Corypheus. Putting aside his apparent ability to create the fake Calling and manipulate the Wardens, he has the Mythal-like power to body-hop into tainted people like Janeka and Larius to control them and save his own life. Does this remind you of anything?
If your mind immediately went to the Archdemon, you're correct. Riordan explains in DAO that Archdemons can hop into any darkspawn to avoid death if they aren't killed by a Grey Warden. The Archdemon cannot seem to possess non-tainted beings, which makes it obvious tainted blood makes possession possible in their case. This tainted blood is also the common denominator between darkspawn, ghouls, and Grey Wardens who can all hear a song, the Calling, something the Mother talks about and something we've seen in action from a darkspawn's point of view in Darkspawn Chronicles. There are also a lot of examples of the Archdemons "whispering" to the darkspawn to be let free of their prisons (and here's a theory on how that prison works) similarly to Corypheus influencing the Wardens in the Vimmark Mountains to break him out of his prison and how Dumat supposedly whispered to Corypheus in his dreams to enter the Fade.
In the Grey Wardens' case, the exact recipe of the joining juice that taints their blood isn't spelled out in canon but we know it consists of lyrium, darkspawn blood, and Archdemon blood. Wardens gain some sort of connection to the Archdemon, hearing its calling and seeing it in their dreams, to the point that some older Wardens claim to understand what it says. All of this sounds very familiar to Dumat's supposed connection to Corypheus and the fake Calling we see firsthand in DAI.
Speaking of lyrium, it seems to have a song of its own. According to World of Thedas Volume 1 (page 40), lyrium in the dwarven language is also called "singing stone." The same thing can be said of red lyrium:
"Those who have touched red lyrium—or even come near it—report that it "sings" to them, like whispers in the mind that slowly drive them mad."
Codex entry: Red Lyrium
Valta speculates that lyrium is the blood of Titans. Now, looking at the pattern above with blood and control, I think it's possible it isn't lyrium itself that sings. It's the Titan singing through the lyrium. This is supported by The Descent:
"Its blood now flows through me, and its song fills the gaps in our history. I close my eyes and see glimpses of the world that was, before everything changed and the dwarven race broke in two. Something caused the Titans to fall, and the fate of my people fell with them. The Titan wants me to know. No, more than that. It wants me to understand. There is a loneliness to its song."
Codex entry: Titans
In the case of red lyrium, i.e. blighted lyrium, it appears to have the ability to influence and control people, which would explain why Bartrand went mad once he acquired the Red Lyrium Idol. Whether the person doing the controlling is specifically a blighted Titan or "merely" someone blighted/tainted is a whole another tangent I don't want to go on right now.
It's interesting that so far only the Titan's song doesn't feel like a sinister, controlling presence. I think it's possible that the theories about the naturally occurring dwarven hivemind are correct and the ancient elves just tried to replicate it as a means of control, who were later copied by the Tevinter Imperium, who were then copied by other humans.
One of the most prominent signs of ownership and control for the ancient elves was vallaslin, i.e. blood writing. They were used as slave markings. The "ink" used for it contains blood and it was etched into the slave's skin as a sign of ownership. World of Thedas Volume 2 (page 201) has an interesting poem that may or may not be relevant here:
"We/it lost eternity or the ruined tree of the People,
Time won't help when the land of dreams is no longer our journey.
We try to lead despite the eventual failure of our markings.
To the inevitable and troubling freedom we are committed.
When we could no longer believe, we lost glory to war.
When the Wolf failed/won, we lost the People to war."
My first instinct was to interpret this from the POV of the Dalish or even ancient elven slaves but the poem gains a different meaning if you pretend it's from the POV of the Evanuris. IMO the "When the Wolf failed/won" line supports both readings.
Does this necessarily mean ancient vallaslin had some kind of control over slaves? Not necessarily but I wouldn't rule out the possibility.
This wasn't the only way the Evanuris exerted control over others so let's take a look at the Well of Sorrows next, specifically its "waters." Codex entry: Here Lies the Abyss draws some parallels between the "emerald waters" of the Well and the Fade:
"From the waters of the Fade you made the world. As the Fade had been fluid, so was the world fixed."
What exactly are the "waters of the Fade"? Is it lyrium or something more? The above lines seem to describe the same dichotomy as "the realm of the dream and the realm of the flesh" quoted further up.
Whatever these waters may be, almost immediately after drinking from them, both Morrigan and the Inquisitor can hear and understand the whispers of the Well and it's stated they can be controlled by Mythal. Here is a separate post about why I think this means Morrigan becomes the next High Priest of Mythal and basically acts as a host for her, i.e. she becomes possessed by the spirit (demon?) of Mythal.
But even with the Evanuris being as powerful spirits/mages as they were, some ancient elves still tried to challenge their rule. The Geldauran's Claim codex entry has an interesting take on these controller/controlled, master/slave relationships in DA:
"There are no gods. There is only the subject and the object, the actor and the acted upon. Those with will to earn dominance over others gain title not by nature but by deed.
I am Geldauran, and I refuse those who would exert will upon me. Let Andruil's bow crack, let June's fire grow cold. Let them build temples and lure the faithful with promises. Their pride will consume them, and I, forgotten, will claim power of my own, apart from them until I strike in mastery."
Codex entry: Geldauran's Claim
This kind of hunger for control would live on even after the fall of Arlathan and the ancient elves, only to show up in the Tevinter Imperium. I've already talked about Corypheus so it's time for a different magister, Danarius.
Recall Fenris who has lyrium markings carved into his body by his former master in a crude imitation of vallaslin. Now think back to Geldauran's words: "There is only the subject and the object, the actor and the acted upon. Those with will to earn dominance over others gain title not by nature but by deed." Fenris is not literally mind-controlled by Danarius but he is very much under his control before he escapes. Danarius enslaved Fenris the same way the Evanuris enslaved their own people and aims to keep him under his control, making this a thematically relevant example.
But wait, there's more! Last we have the Templars who, in order to be able to perform their abilities, take lyrium (again, Titan's blood) into their bodies. They subsequently become addicted to the stuff. In order to feed their addiction, they remain in the Chantry's control. The same Chantry that technically uses a song to control people: the Chant of Light. It's not direct control like Corypheus's powers, of course, but I think it's another example of a copy of a copy of a copy of the real deal and I don't think it's by accident that it's so similar to all of the above.
Here is a short overview of the above theory:
Controller | Controlled | Blood | Song |
Titans | Dwarves | Lyrium (Titan's blood) | Lyrium sings |
Evanuris | Elves | Vallaslin (blood writing) | master-slave control? |
Mythal | Morrigan/The Inquisitor | The "waters" of the Well of Sorrows | The Voices of the Well |
Archdemon | Grey Wardens | Tainted blood | The Calling |
Archdemon | Darkspawn, Ghouls | Tainted blood | The Calling |
Corypheus | Grey Wardens | Tainted blood | The (fake) Calling |
Danarius | Fenris | Lyrium markings | master-slave control? |
The Maker/The Chantry | Templars | Lyrium | The Chant of Light |
TLDR: Blood is a gateway between the Fade and the physical world and it can be used to possess and control others. The "songs" various affected people hear are basically commands from their masters.
In their blood the Maker's will is written, indeed.