Particular concerning origin of people infiltrating group (7)
I believe the answer is:
respect
'particular' is the definition.
(both can mean a detail or matter for consideration)
'concerning origin of people infiltrating group' is the wordplay.
'concerning' becomes 're' (both can mean on a particular topic).
'origin of' indicates taking the first letters.
'infiltrating' indicates putting letters inside.
'group' becomes 'sect' (I've seen this in other clues).
The first letter of 'people' is 'p'.
'p' inserted within 'sect' is 'spect'.
're'+'spect'='RESPECT'
(Other definitions for respect that I've seen before include "Treat with consideration" , "Esteem, deference" , "Avoid offending" , "Point" , "estimation" .)