Comment concerning evangelist (6)
I believe the answer is:
remark
'comment' is the definition.
(a remark is a spoken comment)
'concerning evangelist' is the wordplay.
'concerning' becomes 're' (both can mean on a particular topic).
'evangelist' becomes 'mark' (traditional author of the Gospel of Mark).
're'+'mark'='REMARK'
(Other definitions for remark that I've seen before include "Comment, observation" , "Observation - notice" , "Written or spoken comment" , "Comment or mention" , "Something said; take notice of" .)