Thought about fine lesson read in church (10)
I believe the answer is:
reflection
'thought' is the definition.
(reflection is a kind of thought)
'about fine lesson read in church' is the wordplay.
'about' becomes 're' (regarding).
'fine' becomes 'f' (abbreviation).
'lesson read in church' becomes 'lection' (I've seen this before).
're'+'f'+'lection'='REFLECTION'
(Other definitions for reflection that I've seen before include "serious thought?" , "Mirror image" , "Effect of not absorbing light" , "mental study's required" .)