Messenger of a deity in changeless form (5)

I believe the answer is:

angel

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'messenger of a deity' is the definition.
'angel' can be an answer for 'messenger' (heavenly messenger). I am not certain of the 'of a deity' bit.

'in changeless form' is the wordplay.
'in' says the answer is hidden in the clue.
'ANGEL' can be found hidden inside 'changeless form'.

Can you help me to learn more?

(Other definitions for angel that I've seen before include "Heavenly being - 21 (anag)" , "eg Gabriel" , "Ministering spirit" , "Word linking cake and fish" , "on the Tube?" .)

I've seen this clue in the Sydney Morning Herald.

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