Hail, wedded Love, mysterious law, true source
Of human offspring, sole propriety
In Paradise of all things common else!
By thee adulterous Lust was driven from men
Among the bestial herds to range; by thee
Founded in reason, loyal, just, and pure,
Relations dear, and all the charities
Of father, son, and brother, first were known.
Far be it, that I should write thee sin or blame,
Or think thee unbefitting holiest place,
Perpetual fountain of domestick sweets,
Whose bed is undefiled and chaste pronounced,
Present, or past, as saints and patriarchs used.
Here Love his golden shafts employs, here lights
His constant lamp, and waves his purple wings,
Reigns here and revels; not in the bought smile
Of harlots, loveless, joyless, unendeared,
Casual fruition; nor in court-amours,
Mixed dance, or wanton mask, or midnight ball,
Or serenate, which the starved lover sings
To his proud fair, best quitted with disdain.
These, lulled by nightingales, embracing slept,
And on their naked limbs the flowery roof
Showered roses, which the morn repaired. Sleep on,
Blest pair; and O! yet happiest, if ye seek
No happier state, and know to know no more.

I'm not sure I agree with this: "In other words, yes, by total mutual interpenetration."

Human sex isn't "total mutual interpenetration", it is, to use Milton's language, "restrained conveyance ... as flesh". I'd say Milton is drawing a sharp distinction between what people and angels do. The analogy between the two is limited.

Anyway, I guess it is a sign of the times that readers need to be told that PL is a narrative poem!