The most common and most likely answer to this crossword clue is the 7 letter word HYMNODY
I've seen this crossword clue in The Guardian
H
Y
M
N
O
D
Y
Buddy explains!

The straight part
We know that "singing in church/singing in church" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case singing in church/singing in church = hymnody.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 HYMNODY mean?
HYMNODY noun- The writing, composing, or singing of hymns or psalms.
- The hymns of a particular church or of a particular time.