Preliminarily examine lessons by Catholic church (5)
I believe the answer is:
recce
'preliminarily examine' is the definition.
'lessons by catholic church' is the wordplay.
'lessons' becomes 're' (Religious Education).
'by' means one lot of letters go next to another.
'catholic' becomes 'c' (abbreviation as in RC for Roman Catholic).
'church' becomes 'ce' (abbreviation for Church of England).
're'+'c'+'ce'='RECCE'
(Other definitions for recce that I've seen before include "Informal appraisal" , "Check out" , "See how the land lies (informal)" , "Mil. survey" , "Preliminary survey" .)