There is an assumption that equal opportunity in the hierarchy of the Empire and being Chosen are one in the same. They are not. At no point to my knowledge does Tash-Murkon or any other liberal character explicitly say or argue that non-True Amarr can become Chosen. What they specifically argue for is that non-True Amarr can be and are contributors to the faith and Empire, able to fill important positions in the Imperial hierarchy beyond simple servitude.
There was by the PF a variety of different approaches possible. At least in the Tash-Murkon domains racism seems to be shunned quite blatantly.
Again, the conservatives are more likely to be ethnocentric - no surprise there. Right above, however, the Tash-Murkons say that "The Empire was forged in our collective blood. We worship the one and only Lord God. It is by all our strengths that the Empire was made great, and it will be by all our strengths that it shall continue." Ethnocentrism is clearly not a universally-applied, totally homogenous rule in the faith; if it were, the Murkons' words would be heresy.
And here it's even outright said - pure ethnocentrism/racism exists among the more conservative factions, but is highly controversial and not at all universally accepted in the Empire. If True Amarr being forever the only Chosen was codified in the scriptures, the controversy in the quote would not be occurring.
The common element in all of these is the belief that acknowledging the value of other races automatically means that non-True Amarr can become Chosen. It is entirely possible for a character to argue for equal rights in the hierarchy of the Empire while also believing that only True Amarr are Chosen by God. Belief in one does not presume belief in the other.
In the case of Tanar, the controversy was over his argument that all non-True Amarr are fit only to serve and can hold no titles or other positions of influence. His story does not say anything about Chosen, what it says is that he believed there was Scriptural evidence that mandated that non-True Amarr must only serve and never hold positions of importance.
Essentially, what we have to take from these examples should not be assumed to be 'can other races become Chosen?', when there is also the equally possible argument of 'what kind of influence and rights can non-Chosen have in the Empire?', which is the more likely one in my opinion. I see the acceptance of, say, Khanid Holders not to mean 'Khanid can become Chosen', but instead 'Non-Chosen of proven faith can become Holders'.
The only source that says that anyone can become
Chosen, by that wording, is the Apocryphon. Not the Scriptures, not Tash-Murkon, not canon liberals. The latter three have said things that can be interpreted to mean such, can imply belief in that, but none of them explicitly say it.
I'm not going to say that the belief of becoming Chosen by non-Chosen doesn't exist. I'm sure it does, there's enough leeway to argue for it. But I would imagine such a thing is not open, with arguments instead being focused around responsibilities and opportunities while leaving the issue of 'becoming Chosen' unsaid. Hence why you always only see the conservative NPCs talking about the one true race, chosen by God, while liberals never use that same language about chosen people. They instead talk about societal contributions and strengths and being positive influences on the Empire. If someone outright said 'non-True Amarr are/should also be Chosen' in public discourse, I would see that starting a controversy (
which is what we see with the Kameiras)
True Amarr lead because they were first chosen, but others can achieve glory and recognition by opting to aid the faithful as well. This is little different from the situations of the Eudorians, Khanid, and Ni-Kunni (all of which are not strictly speaking True Amarr, but are at current varying distances along the path to becoming Chosen).
Again, there is an assumption that becoming redeemed/faithful and becoming Chosen are the same thing. I have yet to see a source that says this beyond Apocryphon.
Also, there is still Scripture which says that everyone can be chosen by God:
"All things were created by the Divine, and so the glory of our faith is inherent to us all;
When thine heart shines with the Light, thou shalt know no hardship;
When thine actions are in Light's name, thou art immortal."
- The Scriptures, Book of Trials 2:1
I see nothing here that says that everyone can become Chosen. It says that the glory of faith is inherent in all, which can mean many things. It does not say that all can be God's Chosen. Unless something
explicitly says that non-True Amarr can become Chosen, it is an interpretation. And the only Scripture that explicitly says it is a heretical one.
Actually, the Sabik believe that savants/chosen are born destined for such:
"...the Sani Sabik faith embraced two central dogmas. The first was that certain people were born destined for greatness, with all others existing solely to serve and breed these savants. The second was that immortality was attainable by these savants." - Evelopedia
The issue with 'joining' is that the Sabik were willing to accept anyone who simply followed their ways as inherently Savant; this stands in stark contrast to the traditional Amarr view of Chosen-ness being gained through extended service and faith to the (orthodox) God.
Stated as destiny, but in practice it's meritocratic hence why it appeals to commoners, as it is a method of social mobility that they don't otherwise have. For sects like the Blood Raiders, whether you were destiny is determined by your own efforts, "if you embraced the faith, then you were clearly destined". This is rather different from having your status laid out before you from birth and having no avenue to change it.
As far as "stark contrast to the traditional Amarr view of Chosen-ness being gained through extended service and faith to the (orthodox) God"... uh, no. The traditional Amarr view is that the Chosen are born that way. This is said in that same article. This is where the Sabik and Amarr faiths are similar.
"The second commonality is the belief in savants, individuals who are greater than their fellow man and capable of great achievements. The nature of these savants varies from sect to sect, with some following closely to the Amarr tradition of the chosen being born that way. The Blood Raiders view the practice more liberally, considering anyone strong enough to embrace the Blood Raider lifestyle worthy of being called one of the chosen. Such a belief is found in many of the other sects scattered across New Eden and is especially appealing to Amarr commoners, who seek to rise above their restrictive stations."Being born Chosen is the traditional Amarr belief, as stated here, and the Sabik sects that believe similarly are the ones following closer to the orthodox Amarr religion.