In Byzantine rite, a reluctance to change? (7)
I believe the answer is:
inertia
'reluctance to change?' is the definition.
(I've seen this before)
'in byzantine rite a' is the wordplay.
'byzantine' indicates anagramming the letters (byzantine means complex or confusing).
'rite' anagrammed gives 'erti'.
'in'+'erti'+'a'='INERTIA'
(Other definitions for inertia that I've seen before include "I retain, being without energy" , "Unwillingness to move" , "Tendency not to act" , "Resistance to change" , "Slowness to take action, state of laziness" .)