Noble needs to practise guarding king in church (8)
I believe the answer is:
princely
'noble' is the definition.
(similar in meaning)
'to practise guarding king in church' is the wordplay.
'to practise' becomes 'ply' (as in plying or practising a trade).
'guarding' means one lot of letters goes inside another.
'king' becomes 'r' (r is abbreviation for rex).
'church' becomes 'ce' (abbreviation for Church of England).
'r'+'in'+'ce'='rince'
'ply' placed around 'rince' is 'PRINCELY'.
'needs' is the link.
(Other definitions for princely that I've seen before include "Lavish (like Charles?)" , "Magnificent" , "like Hamlet?" , "(Of a sum) generous" , "In the manner of a regal son" .)