Being sixteen, converted by church (9)
I believe the answer is:
existence
'being' is the definition.
(I know that being can be written as existence)
'sixteen converted by church' is the wordplay.
'converted' is an anagram indicator.
'by' says to put letters next to each other.
'church' becomes 'CE' (Church of England).
'sixteen' anagrammed gives 'existen'.
'existen'+'ce'='EXISTENCE'
(Other definitions for existence that I've seen before include "A way of living" , "State of being" , "The business of being" , "survival" , "Way of life" .)