Herb, one about to be cut from church building (5)
I believe the answer is:
basil
'herb' is the definition.
(basil is a kind of herb)
'one about to be cut from church building' is the wordplay.
'one' becomes 'li' (I've seen this in other clues).
'about' says the letters should be written backwards.
'to' says to put letters next to each other (I've seen this in other clues).
'be cut from church building' becomes 'bas' (I can't explain this - if you can you should give a lot more credence to this answer).
'li' reversed gives 'il'.
'il' after 'bas' is 'BASIL'.
(Other definitions for basil that I've seen before include "Pesto ingredient" , "Herb - Mr Fawlty" , "serially chaotic character" , "Herb (from Fawlty Towers?)" , "Fragrant herb" .)