Huge magnitude of sin? Seems men must go to hell! (11)

I believe the answer is:

immenseness

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

'huge magnitude' is the definition.
'immenseness' can be an answer for 'magnitude' (immenseness is a kind of magnitude). I am unsure of the 'huge' bit.

'sin? seems men must go to hell' is the wordplay.
'sin? seems men' can be anagrammed to 'IMMENSENESS'.
However, I'm not sure how the anagram is indicated.

'of' is the link.

Can you help me to learn more?

I've seen this clue in The Independent.

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