Gospeller cordial but indifferent (8)
I believe the answer is:
lukewarm
'indifferent' is the definition.
(I've seen this before)
'gospeller cordial' is the wordplay.
'gospeller' becomes 'luke' (I've seen this before).
'cordial' becomes 'warm' (similar in meaning).
'luke'+'warm'='LUKEWARM'
'but' is the link.
(Other definitions for lukewarm that I've seen before include "Moist" , "Indifferent" , "Apathetic" , "Half-hearted" , "Tepid, or less than enthusiastic" .)