Faith is embraced by those opposing us (6)
I believe the answer is:
theism
'faith' is the definition.
(I know that theism is a type of faith)
'is embraced by those opposing us' is the wordplay.
'embraced by' indicates putting letters inside.
'those opposing us' becomes 'them' (I've seen this in another clue).
'is' placed within 'them' is 'THEISM'.
(Other definitions for theism that I've seen before include "Belief in a deity" , "Belief in existence of a God revealed to man" , "of faith" , "The doctrine or belief in the existence of a God or gods" , "Belief in a creator" .)