Church with more suitable section of book (7)
I believe the answer is:
chapter
'section of book' is the definition.
(a book may be split into chapters)
'church with more suitable' is the wordplay.
'church' becomes 'ch' (common abbreviation).
'with' means one lot of letters go next to another.
'more suitable' becomes 'apter' (more apt).
'ch'+'apter'='CHAPTER'
(Other definitions for chapter that I've seen before include "Division of book, usually numbered" , "Cathedral body" , "religious assembly" , "Book division - assembly of canons" , "one section of book" .)