Make sense of Christmas poem? (6)
I believe the answer is:
decode
'make sense of' is the definition.
(I've seen this in another clue)
'christmas poem?' is the wordplay.
'christmas' becomes 'dec' (Dec is short for December, the Christmas period).
'poem?' becomes 'ode' (ode is a kind of poem).
'dec'+'ode'='DECODE'
(Other definitions for decode that I've seen before include "Penetrate or solve encrypted message" , "Interpret" , "Decipher, decrypt" , "Unscramble" , "Put in" .)