A sermon delivered at Mount St., Mayfair?

I think it could be either:

Which length description are you looking for?:

4,7

11*

good address

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'a sermon delivered at mount st mayfair?' is the definition.
I know nothing about this answer so I can't tell whether this works.

'sermon delivered at mount st mayfair?' is the wordplay.
I cannot quite understand how this works, but
'sermon' could be 'address' (I've seen this before) and 'address' is located in the answer.
The remaining letters 'good' is a valid word which might be clued in a way I don't understand.
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 Evening Standard.

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