Message left in eastern skiing area (7)
I believe the answer is:
epistle
'message' is the definition.
(thesaurus)
'left in eastern skiing area' is the wordplay.
'left' becomes 'L' (common abbreviation).
'in' means one lot of letters goes inside another.
'eastern' becomes 'e'.
'skiing area' becomes 'piste'.
'e'+'piste'='episte'
'l' put within 'episte' is 'EPISTLE'.
(Other definitions for epistle that I've seen before include "A letter from St Paul" , "Maybe Paul's" , "a for instance" , "Paul's work" , "Letter from a saint" .)