The most common and most likely answer to this crossword clue is the 12 letter word DENOMINATION
I've seen this crossword clue in The Times
D
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More clues leading to the result DENOMINATION
Buddy explains!

The straight part
We know that "Religious group/value" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case religious group/value = denomination.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does DENOMINATION mean?
DENOMINATION noun- The act of naming or designating.
- That by which anything is denominated or styled; an epithet; a name, designation, or title; especially, a general name indicating a class of like individuals
- A class, or society of individuals, called by the same name; a sect or religious subgroup.
- A unit in a series of units of weight, money, etc.