A lot of people don't like the Cleric class and its "my god gives me cool powers." Certainly, that sort of heavy divine involvement doesn't fit all settings, nor does the idea of granting the powers rather ran just performing miracles.
Another option would be the "personal genie" or guardian angel type character common to genre media. Jeannie and Shazzan are examples of this type, but I'm thinking more the smaller, invisible to most imp-type like the Great Gazoo, or in a less helpful mode, the impish would be side kicks of comic book heroes like Bat-Mite or Qwsp.
So when a cleric used a "spell" this would be this spirit/being doing stuff at their request. Why they would have such specific and limited interventions could be explained by them being "in training" or maybe just getting used to the Prime Material Plane.
(You might think this fits even better with the 5e Warlock and their Patrons, and I suppose it could, but their spells seem even less a fit than the clerics for this sort of setup.)
In media, this sort of thing is typically portrayed humorously, but it doesn't have to be. If you did portray it humorously, though, not having other characters be sure of whether the tutelary spirit actually exists or whether the PC is crazy might be amusing.
2 hours ago