The most common and most likely answer to this crossword clue is the 10 letter word CLERESTORY
I've seen this crossword clue in The Daily Telegraph
C
L
E
R
E
S
T
O
R
Y
Buddy explains!

The straight part
We know that "enlightenment for the church" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case enlightenment for the church = clerestory.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 CLERESTORY mean?
CLERESTORY noun- The upper part of a wall containing windows to let in natural light to a building, especially in the nave, transept and choir of a church or cathedral.