The bolded part is a very true observation on your part.
My point is more about the object of the unchangeable Fi faith. You're familiar with how utterly weird Ni is, right? Te is more accessible, but it, too, can be rather spooky when dealing with Ni. I believe the INTJ tertiary Fi gains a very strong feeling of security when NiTe functions smoothly. It is a faith and a trust and a confidence. We trust that Ni will quickly provide reliable perceptions, and that Te will just as quickly sort and organize it and make provide Quality Assurance that we aren't off base. When that Ni clicks, we just go. When we were kids, we were nervous and afraid, but there's something about NiTe that always seems more than up to the task, and Fi eventually trusts that, and that grows into that aura of self confidence.
I think it helps to remember that Fi isn't "feelings" but rather the manner in which one processes feelings. My "feelings" tell me I'm at my happiest when doing something intellectual/logical/challenging/learning/teaching. Most all INTJs will tell you they hardly feel confident at all, but when the topic matter comes up with which they're familiar, suddenly its as if all of that trepidation just disappears. We "just know." There is no fear, just a quiet certainty that even if we make a mistake, it will be easily and painlessly corrected. It's the whole INTJ arrogance thing. The only reason we feel such confidence, such arrogance, is because we are that good, and we've proven it to our toughest critic: ourselves. And the moment we traverse back into an area of knowledge or skills with which we're unfamiliar, we go quiet. We lose the aura of authority. We become a normal schlub.
I should correct you with respect to Ni being the ultimate authority. Ni is merely the first actor, the workhorse. It steps in first, and often solves things without Te or Ti or Fi having to become involved. However, after Ni processes something it is up to Te or Ti or Fi to do something with it. If it's clearly a logistical issue, Te handles it. If it's a fairly complex theoretical issue, Te and Ti jointly handle it (which can make it hard for me to tell the difference, because my experience has trained both to be very skilled and often used). If it's a human issue, my Te and Ti give it a brief glance to make sure there isn't something obvious and objective that would resolve it, at which point Fi is given the final authority, as you might put it. In a weird way, that makes Fi the real final authority, the executive that has delegated responsibility to Ni, Te and Ti, but has to step in and handle matters that cannot be delegated. In the end, Fi knows what is right and will decide it ... but it would really rather not having to decide for itself.
I would say that Fi expresses the core of my faith. It's remarkably rock solid, mostly because it is shielded from having to process mundane concerns by my other processes, and only comes into play for that which it is suited.
With respect to religious guilt, I think it's more that INTJs don't get suckered into guilt. The lack of Fe means we don't become upset due to others' feelings. Fi is thereby very protected from abuse: Ni, and Te, and Ti take care of almost everything, and Fe doesn't toss in a curve ball of taking someone's hissy fit seriously. All that is left is what *I* feel.
I'm wondering what role Ti plays for an INFJ. One would think it would be analogous to the role of Fi for an INTJ, with deleterious results for an immature tertiary, and remarkable talents for a developed tertiary. Perhaps you might be able to enlighten me?
I agree to so much of this within me which is why I follow this thread. The only parts I dont agree to is the unwavering faith of Fi. Hence why my eyes never shut and its like I am forced to see no matter what happens to Fi within me. Fi is just something that is experienced within me, but never really controls an unwaivering faith in something or any beliefs. It does give me an idea of desires and wants, but a Ti-Ni loop is more of what causes a stubborness or unwaivering belief. It comes out as you believe what you want to and I will believe what I want to because I cannot logically see what you say. Provide more input and my stubborness subsides and I am open again. This is where Ne comes in handy and from experience is where Fe doesnt do much as I dont need to be convinced, but presented with more data to process.
Fe seems to try to convince you of something which instead of reacting like Fi/Te does and say "are you trying to convince me of something" I instead fight because of the way its done. My INTJ dad picks this up and responds in a better fashion then I do. With me, if you want something, tell me dont try to convince me. More likely then not I will give in to what you want. I wont change my want, but will allow you to have yours.