Militant god takes a look inside (7)
I believe the answer is:
zealous
'militant' is the definition.
(I've seen this before)
'god takes a look inside' is the wordplay.
'god' becomes 'zeus' (Zeus is an example**).
'takes' means one lot of letters goes inside another.
'look' becomes 'lo'.
'inside' indicates putting letters inside.
'zeus' going around 'a' is 'zeaus'.
'zeaus' placed around 'lo' is 'ZEALOUS'.
(Other definitions for zealous that I've seen before include "Very devoted to a cause" , "Avidly enthusiastic" , "Fervent" , "Showing great energy and enthusiasm" , "Highly enthusiastic" .)