Urge strongly and sincerely (6)
I believe the answer is:
exhort
'urge strongly and sincerely' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for exhort that I've seen before include "Entreat earnestly, urge" , "Strongly urge (someone to do something)" , "Urge or advise strongly" , "Urge, counsel earnestly" , "Urge strongly and sincerely" .)