Struggle to keep faith (4,3)

I believe the answer is:

holy war

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'faith' is the definition.
Both the answer and definition are singular nouns.
Perhaps there's an association between them I don't understand?

'struggle to keep' is the wordplay.
'struggle' becomes 'war' (warring is a kind of struggling).
'to' is a charade indicator (letters next to each other) (I've seen this in other clues).
'keep' becomes 'holy' (I am not sure about this - if you are sure you should believe this answer much more).
'war' after 'holy' is 'HOLY WAR'.

Can you help me to learn more?

(Other definitions for holy war that I've seen before include "Religious conflict" , "Jihad" .)

I've seen this clue in The Sunday Times and The Times.

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