Finished, then came here for explanations of parsing. Thanks, all, for illuminating 6d, 22d, 25a, 7d, 10a, but could someone give a hint about 12?
It was described above as a word rarely seen outside cryptics, but that depends on whether you visit, or read about, churches! (Or edit Wikipedia articles about them, in my case).Perfectly ordinary word. But I don't understand the parsing!
... except that now I come to look again, it's obvious: I keep forgetting that interpretation of "on", and was treating "functions" as a verb. All is now clear.
An enjoyable puzzle. FOI: 16a
LOI: 10a (whole NE corner was blank after everything else was complete).
COD: maybe 7d for elegance, though it was my last-but-one (actually solved by my husband, whose main earlier contribution had been an incorrect "away" for 23d which made me struggle with 23a and 25a).