The cabalist is a mix of two different ideas I had for Pathfinder, fused together into one class.
The first idea was called a “Theurge”, and was a planned character for the unreleased Path of Blood book. It was a master of the mind, body, and soul, and had a mix of support and control options depending on options taken. It used spellcasting (it was an 0-6 caster like bards) to support allies or equally debuff enemies, though its most powerful abilities were tied to a “link” it could form to others, which had to be a mental, physical, or spiritual link (which altered its effects depending on which link you used).
The second idea was a “Ritualist”, which was the occult-themed class planned for Paths of Magic. It was intended to have a dark/eldritch theme, using powers that “it didn’t really understand”. It was to focus heavily on powers that were at-will but had a cost: for example, casting deeper darkness but blinding yourself for a round. As part of this, it would have the ability to cast some spells “normally” by using the occult ritual rules, giving it a broad utility capability when out of combat.
After I determined that Path of Blood was getting skipped, I thought of ways to repurpose the mechanics and concepts of some of the planned content for that book, one of which was the theurge class. The mind/body/soul theme is a pretty cool concept to design around, and I wanted to try and still use it somewhere. The ritualist seemed like a good place for it, since dark and forbidden rituals often involve toying with the mind, body, or soul in like…every story about dark and forbidden rituals. Well, except the ones that summon demons and monsters (though more on that later).
The current cabalist started off also being called the ritualist, with many of the same ideas. With the ritualist name, having additional bonuses to occult ritual casting, along with new means to use them, was a clear goal for the class. I tried to keep most of the other ritualist mechanics (that being, inflicting statuses on yourself to cast powers) but themed around manipulating the mind/body/soul combo from Theurge. However, it became quickly apparent that most players aren’t interested in that sort of thing. Maybe as an option you can take, but not for the whole class’s design—unsurprisingly, players don’t like getting weaker to use their best options.
A new mechanic was needed for the class, and almost immediately I settled on a stance-based mechanic. I’ve always been a big fan of stance mechanics, but never really felt Pathfinder did them all that well; the closest it gets to the idea are Style feats, but it’s usually never worth actually switching styles mid-combat (most characters can hardly afford the sheer number of feats to make two styles work in the first place). So having the stances baked-in to the class, with all the needed mechanics to have it work, was the new goal for its design.
The stances were originally “trances”, and consisted of formless body, opened mind, and unyielding soul stances. Body was physically oriented, mind was focused on defense and skills, while soul was sort of magically-built and a bit of a grab-bag of abilities. At this point, the class was being designed as more of a religious theme; it was a divine caster, not a psychic caster, and was more about appealing to deities for strength through rituals. As the design moved forward, though, trying to keep this sort of morally-neutral theme (and creating abilities that would make equal sense for evil deities as good ones) was proving very difficult. The designs of the abilities was frequently drifting to a more occult/eldritch theme, which I repeatedly tried to pull back to maintain the divine theme. Eventually, I was convinced by some of my friends to see the design to its logical conclusion, which shifted its whole narrative from religious occultism to eldritch/cosmic occultism. The class is much more cohesively themed for it, I think, so it was definitely the right call.
However, there was still the problem of the stances themselves. Even with the new-found focus on eldritch and cosmic horror, making solid identities for the three stances was proving difficult. The body stance was working fine, and soul was…passable, but the mind stance was struggling to find use. A defensive-oriented path only gets you so far by itself, and with the class’s primary offensive capabilities being pushed into either body (for melee combat) or soul (for spells), it was clearly the weakest of the three.
Rather than trying to keep all three stances, we decided to drop the Soul stance and move to just two: body and mind. The justification for this was that most cosmic horror doesn’t really recognize the soul/spirit as a major theme (being largely an undermining of human faith in a just or moral world), so why would the eldritch-themed class have it as an option? By condensing it to just two stances, we were able to make both feel equally useful, spreading offensive and defensive capabilities between the two but from different directions (body stance being physical offense and defense, and mind stance doing the same for magic).
The different “insights” for each binding were, of course, the main draw to the class, so they had to be pretty flexible and also flavorful. Many were obvious choices, like giving natural attacks or resistances to certain effects. I managed to bring back the “debuff yourself for power” options through a few insights based around confusing yourself, which is risky but interesting. I had a lot of fun designing and re-tooling effects to be more eerie and unnerving: the Erratic Motion insight, for example, could easily have been just a sudden burst of speed, but having it be a weird slide (like the Kos Parasite from Bloodborne, if you’re familiar with it) took an otherwise useful-but-standard effect and gave it a much cooler theme.
Beyond that, it was rounding out the ritual theme and giving some supporting mechanics. I had to bend the rules a bit for occult rituals to work for the class (normally they’re only 4th level and up, and the DCs are like 25 + level, which is WAY too high for early game) but I think we managed a good solution. Most of its non-binding features were just means to make it better at these rituals, which, given the fact it’s one of the only classes that can make its own rituals, felt pretty appropriate.