I'd be careful with this, as though the intent may be noble, it can dissuade a reader into being invested in a character.
It takes away agency from the characters actions, be it wrong or right, thereby making them unrelatable. It wasn't "them" who "saved the day", but rather that it was always meant in such a way; there is no struggle or choice if the choice is already made for them. Without struggle, both within and without, there is no story.
I am not saying this cannot be done, for there are no true "rules" in fictional writing, but there are things to keep in mind: namely the audience. To grab their attention, and drag it along from beginning to end is paramount to any successful story no matter its content. This all depends on who your target audience is, and understanding them. It will need finesse; these characters will need to be challenged not just by external forces, but by their own inner, human senses. You have to know your audience, place them in your characters' shoes by putting yourself among them.
I, too, have been working on a (space fantasy)setting with religious themes for the past ~10 odd years. One of the hardest lessons I've learned, being an autodidact, is to avoid picking up bad habits. One of mine was going off on long, overly-descriptive tangents that distracted from the plot progression(AKA "worldbuilder's disease.")
My advice to you would be to take it slow. Write every day, find your own unique style and prose, and decide who you are writing for. Of course the best authors always write for themselves first; if they don't like it, who will? However, that does not undermine the importance of others who will read it. Know them, understand what they would want to read, and develop your story from there.
For example, things which may appeal to an already-religious audience could be off-putting to a curious, but non-religious audience. If your goal is to use your work as a subtle way to evangelize, then you will have to practice just that - subtlety. Keep your themes between the lines, not heavy-handed/ham-fisted. Conversely, that which is written to reach out to a non-religious audience may be distasteful to those already faithful. You are never going to please everybody, which is why a target audience is necessary. Whatever your audience, the last thing you want to do is annoy or insult your audience.
To go back to the highlighted example: those already religious probably would not mind this as they can relate to this and understand it well, but such a thing would not draw in anyone who does not see things this way. In a most blunt sense, such characters would be seen as "mary sues", which boils down to a character that is not only unchallenged, but has no agency to their actions and whatever potential challenges they could face.
In the end, write what you want to write, but be shrewd and tactful for writing is, no matter the means or methods, a form of communication. To summarize; what is your goal? Who is your audience?
Also, for a bit of advice on how to organize a pre-write, is to decide on an ending first. After that, work on the beginning(the beginning is the hardest part for a writer without an existing following, because it does not matter how good the rest of a story is if they're yawning by the first few pages. Why do you think the pilot episodes of TV shows are often full of action and adrenaline?) You have to get the buns on the plate before you can grab the burger.
In a fantasy setting, allegorical or not, creative liberties will have to be taken. Otherwise the story serves no purpose and may as well not be written. It's the literary equivalent of having two copies of the same painting decorating the same wall.