The generous universe

now glow'd the Firmament
With living Saphirs: Hesperus that led [ 605 ]
The starrie Host, rode brightest, till the Moon
Rising in clouded Majestie, at length
Apparent Queen unvaild her peerless light,
And o're the dark her Silver Mantle threw.

This lovely passage in Book IV serves as the transition from day to evening to night, with the glow of the "living Saphirs" granting pride of place to Hesperus, the evening star -- we might recall the evocation of the same star, but charged with Christian significance, in Lycidas:

So sinks the day-star in the Ocean bed,
And yet anon repairs his drooping head,
And tricks his beams, and with new-spangled Ore, [ 170 ]
Flames in the forehead of the morning sky:

In this pre-Christian, unfallen moment, Hesperus cedes her lead to the mutable moon which, even as it rises, undergoes bewitching tranformation, from veiled Majestie to naked, dominant queen of the night, throwing her silver mantle over the dark. So there are at least four levels of light in this one brief passage, with the unveiling of the moon occurring in unison with the mantling of the earth. (Prof. Rogers noted how in Lycidas there's a tantalizing ambiguity near the end, where the grammar allows for either the sun, or the singer/shepherd, to have "twitch'd his Mantle blew.")

As several of us noted, there is undeniably an element of Fairie, of Midsummer Night and Ariel, in this portion of the poem.

The sense of a world alive with spirit-presences carries forward with Adam's next response to Eve's question about the stars:

But wherfore all night long shine these, for whom
This glorious sight, when sleep hath shut all eyes?

Adam says:

Millions of spiritual Creatures walk the Earth
Unseen, both when we wake, and when we sleep:

And

 how often from the steep [ 680 ]
Of echoing Hill or Thicket have we heard
Celestial voices to the midnight air,
Sole, or responsive each to others note
Singing thir great Creator

They hear a lot of night music - as Pythagoras once suggested we once could hear the Music of the Spheres, until it faded.

As discussed, Adam and Eve are in some ways childlike - they know nothing of death, law, or taxes. Property does not loom large; all creatures possess the earth, air, and seas. It is in that first wonderment, the musings of the child, that Milton chooses to situate a sense of utter plenitude - a universe that is seething, infinite, not simply in size, but in populations - teeming with birds, insects, stars.

This apprehension of Being as the opposite of Void - of an overflowing generousness of creative power -- is not uncommon in early myth, and seems to be almost a working hypothesis of any poet you name, be it Hesiod, Shakespeare, or Whitman. It's also, if this is not too Borgesian to suggest, the preferred hypothesis of the Standard Model of particle physics and of string theory. That is to say, our advanced scientific probings of the universe find wheels within wheels, quarks within atoms, strings within all things.