Upset, remove lessons in religion for all time (8)
I believe the answer is:
evermore
'for all time' is the definition.
(thesaurus)
'upset remove lessons in religion' is the wordplay.
'upset' indicates anagramming the letters.
'lessons in religion' becomes 'RE' (Religious Education).
'remove' anagrammed gives 'evermo'.
'evermo'+'re'='EVERMORE'
(Other definitions for evermore that I've seen before include "(For) perpetuity" , "To all eternity" , "For which, permanently" , "Forever (literary)" , "unceasingly" .)