Churchmen wave its arms (7)

I believe the answer is:

marists

I'm a little stuck... Click here to teach me more about this clue!

'churchmen wave' is the definition.
I don't know anything about this answer so I can't judge whether this works.

'its arms' is the wordplay.
I cannot quite understand how this works, but
an anagram of 'its' is 'ist' which is present in the answer.
an anagram of 'arms' is 'mars' which is located in the left over letters.
No letters remain.
This may be the basis of the clue (or it may be nonsense).

Can you help me to learn more?

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

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