Religious set's guide (5)
I believe the answer is:
pilot
'guide' is the definition.
(piloting is a kind of guiding)
'religious set's' is the wordplay.
'religious' becomes 'pi'.
'set' becomes 'lot' ('lot' can be a synonym of 'set').
'pi'+'lot'='PILOT'
(Other definitions for pilot that I've seen before include "He steers ship or plane" , "Guide, steer" , "Ship's guide" , "This person can be found in a plane or a boat" , "Airman" .)