Reason to accept court's goodness (8)
I believe the answer is:
sanctity
'goodness' is the definition.
(I have seen 'Great goodness' mean 'sanctity' so perhaps 'goodness' could also mean 'sanctity')
'reason to accept court's' is the wordplay.
'reason' becomes 'sanity' (I've seen this before**).
'to accept' means one lot of letters goes inside another.
'court' becomes 'ct'.
'sanity' going around 'ct' is 'SANCTITY'.
(Other definitions for sanctity that I've seen before include "Holy or sacred state" , "Condition of holiness" , "State of grace and holiness" , "Ultimate importance" , "Saintliness" .)