Blocking passage in church, one wet behind ears (5)
I believe the answer is:
naive
'wet behind ears' is the definition.
(I've seen this before)
'blocking passage in church one' is the wordplay.
'blocking' means one lot of letters goes inside another.
'passage in church' becomes 'nave' (nave means a part of a church).
'one' becomes 'I' (Roman numeral).
'nave' going around 'i' is 'NAIVE'.
(Other definitions for naive that I've seen before include "Innocently trustful" , "Green, inexperienced" , "Lacking guile" , "Natural, unaffected" , "Excessively trusting or innocent" .)