Moral slip-up first ignored in part of the church? (4)
I believe the answer is:
apse
'part of the church?' is the definition.
(part of a church building)
'moral slip-up first ignored' is the wordplay.
'moral slip-up' becomes 'lapse'.
'first ignored' means to remove the first letter.
'lapse' with its initial letter taken off is 'APSE'.
'in' acts as a link.
(Other definitions for apse that I've seen before include "place in church" , "Peas (anag) -- part of a church" , "Architectural feature in a church" , "Large recess in church" , "Recess in church wall" .)