Everlasting variety for Peter and Paul (9)
I believe the answer is:
'everlasting' is the definition.
'variety for peter and paul' is the wordplay.
'variety for' indicates anagramming the letters.
'and' says to put letters next to each other.
'peter' after 'paul' is 'paulpeter'.
'paulpeter' anagrammed gives 'PERPETUAL'.
(Other definitions for perpetual that I've seen before include "Endless, lasting" , "Going on for ever" , "Nonstop" , "Going on forever" , "Perennial" .)