Expatiate and agree to differ about the origins of natural law (7)
I believe the answer is:
enlarge
'expatiate' is the definition.
(I've seen this before)
'agree to differ about the origins of natural law' is the wordplay.
'to differ' is an anagram indicator.
'about' is an insertion indicator.
'the origins of' indicates taking the first letters.
The first letters of 'natural law' is 'nl'.
'agree' is an anagram of 'earge'.
'earge' placed around 'nl' is 'ENLARGE'.
'and' acts as a link.
(Other definitions for enlarge that I've seen before include "Gleaner (anag.)" , "go into greater detail" , "Amplify" , "Grow" , "Blow up" .)