In Book 3, when God appears for the first time, Milton describes him as a "fountain of light"—a rich instance of imagery that also includes a paradox:
Thee Father first they sung omnipotent,
Immutable, immortal, infinite,
Eternal King; thee Author of all being,
Fountain of light, thyself invisible
Amidst the glorious brightness where thou sitt’st
Throned inaccessible, but when thou shad’st
The full blaze of thy beams, and through a cloud
Drawn round about thee like a radiant shrine,
Dark with excessive bright thy skirts appear,
Yet dazzle Heav’n, that brightest Seraphim
Approach not, but with both wings veil their eyes.
God is not even visible on his throne, which is made of "glorious brightness," since he himself is made of blazing "beams," seemingly brighter than the sun, with a "cloud" wrapped around him "like a radiant shrine" (leading Seraphim to cover their eyes with their wings): this imagery is meant to show that God's brilliance, divinity, and authority are unmatched, but also potentially dangerous (the Seraphim could blind themselves if they looked directly at him, as one would from looking at the sun for too long).
Paradoxically, God's robes are "Dark with excessive bright"—in other words, so bright that they appear dark, passing from one end of the spectrum to the other: this paradox both underscores God's brilliance and power, but also shows that not all in Heaven is lightness and serenity. God has a dark side to him, too—as demonstrated by the punishments he enacts against those who disobey him.
In Book 4, as Satan journeys to Paradise, he experiences "many doubts with himself" (as Milton notes in his preface to the Book), which he voices in a soliloquy that features a paradox:
Nay curs'd be thou; since against his thy will
Chose freely what it now so justly rues.
Me miserable! which way shall I fly
Infinite wrath, and infinite despair?
Which way I fly is Hell; my self am Hell;
And in the lowest deep a lower deep
Still threatening to devour me opens wide,
To which the Hell I suffer seems a Heav'n.
O then at last relent: is there no place
Left for repentance, none for pardon left?
Previously, Satan has seemed ebullient and confident—proud of his decision to defy God and rebel against Heaven—but as he reaches Paradise, he begins to experience regret: not merely because he has been cast out of Heaven and lost God's favor, but because he feels he is "Hell" himself: irredeemably evil. This soliloquy shatters the reader's prior expectations for Satan, humanizing him as a character: as a tragic, multi-dimensional hero, he is not purely evil, but experiences chagrin and self-doubt, too.
Paradoxically, Satan likens the "Hell" he is suffering to "a Heav'n"—harkening back to what he has told Beelzebub earlier (in Book 1: "the mind is its own place, and in itself can make a heav'n of hell, a hell of heav'n"), as if to remind himself that he must accept his confinement in Hell, and attempt to seize power during his exile, treating Hell as if it were a Heaven.
This soliloquy—like another Satan soliloquy later in Book 4, after he spots Adam and Eve and experiences "love" for them—becomes a vehicle for Satan to work out and articulate his complicated emotions, while instructing himself to shore up courage and carry out his plot in Eden.
In Book 4, Adam and Eve are introduced—naked and majestic—in an extended descriptive passage that features a paradox:
A whole day’s journey high, but wide remote
From this Assyrian garden, where the Fiend
Saw undelighted all delight, all kind
Of living creatures new to sight and strange:
Two of far nobler shape erect and tall,
Godlike erect, with native honour clad
In naked majesty seemed lords of all,
And worthy seemed, for in their looks divine
The image of their glorious Maker shone,
Truth, wisdom, sanctitude severe and pure,
Severe, but in true filial freedom placed;
Whence true authority in men; though both
Not equal, as their sex not equal seemed;
For contemplation he and valour formed,
For softness she and sweet attractive grace,
He for God only, she for God in him...
Adam and Eve are of "far nobler shape erect and tall" than the other animals in Eden, demonstrating their clear (pre-Fall) superiority. (That Milton repeats "erect" to specify their divine origins—"Godlike erect"—emphasizes their status and splendor: Milton's narrator almost seems to be witnessing Adam and Eve himself and searching for the right words to describe them.)
Notably, Adam and Eve are "clad" with "naked majesty": though they are literally unclothed (since nudity is not shameful before the fall of man), their "majesty" is as apparent on them as any piece of clothing would be.
This paradox allows Milton to subtly highlight Adam and Eve's nakedness (which would have been a provocative subject to explore and depict in the era in which he was writing)—"naked majesty" could also mean "unadorned majesty" or "stark majesty"—while simultaneously emphasizing the power of their divinely made forms.