Blessedness of bishop with key position, so to speak (9)
I believe the answer is:
beatitude
'blessedness' is the definition.
(I know this)
I can't explain the remainder of the clue.
(Other definitions for beatitude that I've seen before include "supreme happiness" , "Blessedness" , "A tube tied up for heavenly happiness" , "Bliss; 'Blessed are...' verse" , "great happiness" .)