Division in the church? I'll say! (5)
I believe the answer is:
aisle
'division in the church?' is the definition.
(walkway through a church)
'i'll say' is the wordplay.
'say' shows a homophone (sound like).
'ill' is a homophone of 'AISLE'.
(Other definitions for aisle that I've seen before include "Passage between pews" , "that would-be bride hopes to make it up!" , "A key" , "Division of the nave in church" , "Walkway between seats" .)