Comment about gospeller (6)
I believe the answer is:
remark
'comment' is the definition.
(a remark is a spoken comment)
'about gospeller' is the wordplay.
'about' becomes 're' ('re' means regarding or about).
'gospeller' becomes 'Mark' (Gospel according to Mark).
're'+'mark'='REMARK'
(Other definitions for remark that I've seen before include "Comment, observation" , "Notice or comment on" , "Notice; happen to say" , "Written or spoken comment" , "Say as a comment" .)