A good and upstanding prophet concurs (6)
I believe the answer is:
agrees
'concurs' is the definition.
('agree' can be a synonym of 'concur')
'a good and upstanding prophet' is the wordplay.
'good' becomes 'g' (abbreviation).
'and' is a charade indicator (letters next to each other).
'upstanding' shows that the letters should be reversed in order.
'prophet' becomes 'seer' (both can mean someone who tells the future).
'seer' reversed gives 'rees'.
'a'+'g'+'rees'='AGREES'
(Other definitions for agrees that I've seen before include "Assents, concurs" , "Is of one mind" , "Accedes or concurs" , "Shakes hands" , "Holds the same opinion" .)