As you've said, spirituality is a client factor- it's one piece of the whole picture that makes up the client's occupational profile. Prayer, Reiki, Meditation etc. are all interventions, but spirituality itself is something that is dependent on the client and will always be unique to the individual. It should be considered along with every other client factor in the framework (beliefs, values, body structures etc.) in formulating goals and interventions to meet those goals, no matter what the practice setting or type of client.
For your example of helping a client become independent in dressing for church, it depends on what it is about the client that is hindering that task- is it a problem with cognition and sequencing? Maybe that client is being treated in a mental health setting. Is it a child with tactile sensory issues who is oversensitive to the texture of the fabric or the feel of the tag on his shirt? Pediatrics. Somebody with motor planning issues who is physically having trouble performing the movements it takes to get dressed? Phys-dys. It could be so many things... it's impossible to generalize. Those are all deficits that the OT can address.
But the actual importance of getting ready to go to church on the client's part? That's one ADL (dressing) that the client is struggling with that is part of the larger IADL of religious observance which may be tied in with spiritual beliefs. OT is all about the "doing" in life, so in practice, the OT is going to help the client do the tasks he or she needs to do in order to do activities that tie into his or her spirituality (if it is important and meaningful for the client).
Also- if you have a copy of Willard and Spackman (aka the bible of OT), check out chapter 9 written by Christy Billock. A couple quotes from that chapter:
"Occupations that are deeply meaningful to the person, imbued with personal reflection and intention, and carried out within a supportive contextual environment offer the highest potential for spiritual experience."
"Those who practice therapeutic use of self through active listening, empathy, tolerance, unconditional acceptance, and flexibility toward the client's desires and needs demonstrate a spiritual approach to therapeutic interaction."
... I suppose I'm not really understanding the question, but I wish you luck.