Communist, commander without a set of beliefs (5)
I believe the answer is:
credo
'a set of beliefs' is the definition.
(I've seen this before)
'communist commander without' is the wordplay.
'communist' becomes 'red' (red can informally mean communist).
'commander' becomes 'co' (short for commanding officer).
'without' indicates putting letters inside.
'red' inserted into 'co' is 'CREDO'.
(Other definitions for credo that I've seen before include "Words of believer" , "Words to live by; belief" , "Section of mass" , "One's system of beliefs" , "ideology" .)