There’s lots of room for variation here but from what I’ve heard on here and from INFJs I know IRL, doubt and skepticism run deep within us. Each INFJ has their own set of personal beliefs and how much they stick to those beliefs depends on the INFJ for sure. I’ve read descriptions that archetype us as ‘conspiracy theorists’ because of how skeptical we can be. Yet at the same time many of us are very gullible. One of our many contradictions :) It has a lot to do with the open-mindedness of the particular INFJ.
But yes, I’d say it’s typical of many INFJs to question the status quo, question authority, doubt the knowledge that has been presented to us and doubt tradition, all of which are major factors in religious practice. Lots of Intuitive types question tradition and the status quo. I know a lot of INTJs who do this a lot too. Introverted Intuition’s mystical nature seeks it’s own answers, not the answers of the past like Si. I think that combined with our theory calculating Ti, it gives INFJs a prime arsenal to concoct very specific and personal belief systems. Ones that are subject to the reevaluating and perfectionizing focus of the Ni.
I like to think of the INFJ’s Ni-Ti loop as a great analytical tool. I’d say it’s what makes us one of the most highly self-analytical types out there (hence all the MBTI obsession). Analyzing people and ourselves is one of our strongest gifts so why not analyze the meaning of our existence too while we are at it? Spirituality can mean many different things to different INFJs but you can probably bet that they’ve put in a lot of time analyzing it :)
Like if you’re a skeptical INFJ!