Clergyman the first person to enter church (8)
I believe the answer is:
minister
'clergyman' is the definition.
(minister is a kind of clergyman)
'first person to enter church' is the wordplay.
'first person' becomes 'I' (first-person pronoun).
'to enter' is an insertion indicator.
'church' becomes 'minster' (minster is a kind of church).
'i' placed into 'minster' is 'MINISTER'.
'the' acts as a link.
(Other definitions for minister that I've seen before include "Churchman" , "Tend" , "Cabinet member" , "Parson" , "supply as before" .)