Analysis of Sonnet 74: I Never Drank

I never drank of Aganippe well,
Nor ever did in shade of Tempe sit,
And Muses scorn with vulgar brains to swell;
Poor layman I, for sacred rites unfit.

Some do I hear of poets' fury tell,
But (God wot) wot not what they mean by it:
And this I swear by blackest brook of hell,
I am no pick-purse of another's wit.

How fall it then, that with so smooth an ease
My thoughts I speak, and what I speak doth flow
In verse, and that my verse best wits doth please?

Guess we the cause. 'What, it it thus?' Fie, no.
'Or so?' Much less. 'How then?' Sure, thus it is:
My lips are sweet, inspir'd with Stella's kiss.