Mysterious quality of classical Italian church (7)
I believe the answer is:
romance
'mysterious quality' is the definition.
(I've seen this before)
'classical italian church' is the wordplay.
'classical italian' becomes 'Roman' (someone from Rome).
'church' becomes 'CE' (abbreviation for Church of England).
'roman'+'ce'='ROMANCE'
'of' acts as a link.
(Other definitions for romance that I've seen before include "Novel - love story" , "Court" , "marriage?" , "Sentimental affair in Menorca" , "Love-story" .)