Satan lands atop Mount Niphates, just north of Paradise, the Garden of Eden. He becomes gripped with doubt about the task in front of him; seeing the beauty and innocence of Earth has reminded him of what he once was. He even briefly considers whether he could be forgiven if he repented. But Hell follows him wherever he goes—Satan is actually the embodiment of Hell. If he asks the Father for forgiveness, he knows it would be a false confession; he reasons that if he returned to Heaven, he still could not bear to bow down. Knowing redemption or salvation cannot be granted to him, he resolves to continue to commit acts of sin and evil. He does not notice that during his internal debate, he has inadvertently revealed his devilish nature. He is observed by Uriel, the archangel he tricked into pointing the way. Uriel notices his conflicting facial expressions, and since all cherubs have permanent looks of joy on their faces, Uriel concludes that Satan cannot be a cherub.
Satan now approaches Eden, which is surrounded by a great thicket wall. He easily leaps over it like a wolf entering a sheep’s pen. Inside he sees an idyllic world, with all varieties of animals and trees. He can see the tallest of the trees, the Tree of Life—and next to it, the forbidden Tree of Knowledge. He perches himself on the Tree of Life, disguised as a cormorant, a large sea bird. Finally, he notices two creatures walking erect among the other animals. They walk naked without shame, and work pleasantly, tending the garden. Satan’s pain and envy intensifies as he sees this new beautiful race, created after he and his legions fell. He could have loved them, but now, his damnation will be revenged through their destruction. He continues to watch them, and the man, Adam, speaks. He tells Eve not to complain of the work they have to do but to be obedient to God, since God has given them so many blessings, and only one constraint: they must not eat the fruit of the Tree of Knowledge. Eve agrees wholeheartedly, and they embrace.
Eve tells Adam of her first awakening as she came to life and how she wondered who and where she was. She found a river and followed it upstream to its source. Her path led to a clear, smooth lake, and Eve looked into the lake, seeing an image in its surface, which she soon discovers is her own. She hears a voice explaining to her that she was made out of Adam, and with him she will become the mother of the human race. Overlooking Adam and Eve, Satan sees his opportunity. If the Father has given them a rule to follow, then they might be persuaded to break it. He leaves the two for a while, going off to learn more from other angels.
Meanwhile, Uriel comes before the Archangel Gabriel, at the gate of Eden, and tells him about the shape-changing spirit that he saw from the hilltop. They both suspect that it might be one of the fallen ones. Gabriel promises that if the spirit is in the garden, they will find it by morning. Around this time, Adam and Eve finish their day’s work. They go to their leafy bower, praising God and each other for their blissful life, and after a short prayer, they lie together—making love without sin, because lust had not yet tainted their natures.
Night falls, and Gabriel sends search parties into the Garden. Two of his angels find Satan, disguised as a toad, whispering into the ear of Eve as she sleeps. They pull him before Gabriel, who recognizes him, and demands to know what he is doing in Paradise. Satan at first feigns innocence, as they have no proof that he means harm. But Gabriel knows him to be a liar, and threatens to drag him back to Hell. Enraged by this threat, Satan prepares to fight him. The two square off for a decisive battle, but a sign from Heaven—the appearance in the sky of a pair of golden scales—stops them. Satan recognizes the sign as meaning he could not win, and flies off.
As Book IV opens, Milton presents Satan as a character deeply affected by envy and despair. Earlier in the poem, Satan seems perfectly confident in his rebellion and evil plans. His feeling of despair at the beauty of Paradise temporarily impairs this confidence. While in Hell, Satan tells himself that his mind could make its own Heaven out of Hell, but now he realizes that the reverse is true. As close to Heaven as he is, he cannot help but feel out of place, because he brings Hell with him wherever he goes. For Satan, Hell is not simply a place, but rather a state of mind brought on by a lack of connection with God. Satan’s despondent recognition of this fact corresponds with what Milton sees as the worst sin of all: despair. If even this beautiful new world cannot make Satan forget Hell, then he can never hope to seek forgiveness and return to Heaven. As the Bible says, the one sin that cannot be forgiven is despairing of forgiveness; if one cannot even ask for mercy, it cannot be granted. Satan realizes this, and decides that the only course of action is to enjoy his own wickedness, and pursue it with all his strength. Milton preempts the crucial question of whether Satan could have successfully repented back in Book III. There, God said that he would give grace to humankind because Satan would prompt humankind’s sin. But he would not help the fallen angels, and especially Satan, because their sin came out of themselves and from no other source.