From "Manual of Muad'Dib" by the Princess Irulan

We're trapped here , she agreed.
And she accepted the truth of his words. No pressure of the Bene Gesserit, no trickery or artifice could pry them completely free from Arrakis: the spice was addictive. Her body had known the fact long before her mind awakened to it.
So here we live out our lives , she thought, on this hell-planet. The place is prepared for us, if we can evade the Harkonnens. And there's no doubt of my course: a broodmare preserving an important bloodline for the Bene Gesserit Plan .
"I must tell you about my waking dream," Paul said. (Now there was fury in his voice.) "To be sure you accept what I say, I'll tell you first I know you'll bear a daughter, my sister, here on Arrakis."
Jessica placed her hands against the tent floor, pressed back against the curving fabric wall to still a pang of fear. She knew her pregnancy could not show yet. Only her own Bene Gesserit training had allowed her to read the first faint signals of her body, to know of the embryo only a few weeks old.
"Only to serve," Jessica whispered, clinging to the Bene Gesserit motto. "We exist only to serve."
"We'll find a home among the Fremen," Paul said, "where your Missionaria Protectiva has bought us a bolt hole."
They've prepared a way for us in the desert , Jessica told herself. But how can he know of the Missionaria Protectiva? She found it increasingly difficult to subdue her terror at the overpowering strangeness in Paul.
He studied the dark shadow of her, seeing her fear and every reaction with his new awareness as though she were outlined in blinding light. A beginning of compassion for her crept over him.
"The things that can happen here, I cannot begin to tell you," he said. "I cannot even begin to tell myself, although I've seen them. This sense of the future—I seem to have no control over it. The thing just happens. The immediate future—say, a year—I can see some of that . . . a road as broad as our Central Avenue on Caladan. Some places I don't see . . . shadowed places . . . as though it went behind a hill" (and again he thought of the surface of a blowing kerchief) " . . . and there are branchings . . . "
He fell silent as memory of that seeing filled him. No prescient dream, no experience of his life had quite prepared him for the totality with which the veils had been ripped away to reveal naked time.
Recalling the experience, he recognized his own terrible purpose—the pressure of his life spreading outward like an expanding bubble . . . time retreating before it . . .
Jessica found the tent's glowtab control, activated it.
Dim green light drove back the shadows, easing her fear. She looked at Paul's face, his eyes—the inward stare. And she knew where she had seen such a look before: pictured in records of disasters—on the faces of children who experienced starvation or terrible injury. The eyes were like pits, mouth a straight line, cheeks indrawn.
It's the look of terrible awareness , she thought, of someone forced to the knowledge of his own mortality .
He was, indeed, no longer a child.
The underlying import of his words began to take over in her mind, pushing all else aside. Paul could see ahead, a way of escape for them.
"There's a way to evade the Harkonnens," she said.
"The Harkonnens!" he sneered. "Put those twisted humans out of your mind." He stared at his mother, studying the lines of her face in the light of the glowtab. The lines betrayed her.
She said: "You shouldn't refer to people as humans without—"
"Don't be so sure you know where to draw the line," he said. "We carry our past with us. And, mother mine, there's a thing you don't know and should—we are Harkonnens."
Her mind did a terrifying thing: it blanked out as though it needed to shut off all sensation. But Paul's voice went on at that implacable pace, dragging her with it.
"When next you find a mirror, study your face—study mine now. The traces are there if you don't blind yourself. Look at my hands, the set of my bones. And if none of this convinces you, then take my word for it. I've walked the future, I've looked at a record, I've seen a place, I have all the data. We're Harkonnens."
"A . . . renegade branch of the family," she said. "That's it, isn't it? Some Harkonnen cousin who—"
"You're the Baron's own daughter," he said, and watched the way she pressed her hands to her mouth. "The Baron sampled many pleasures in his youth, and once permitted himself to be seduced. But it was for the genetic purposes of the Bene Gesserit, by one of you ."
The way he said you struck her like a slap. But it set her mind to working and she could not deny his words. So many blank ends of meaning in her past reached out now and linked. The daughter the Bene Gesserit wanted—it wasn't to end the old Atreides-Harkonnen feud, but to fix some genetic factor in their lines. What? She groped for an answer.
As though he saw inside her mind, Paul said: "They thought they were reaching for me. But I'm not what they expected, and I've arrived before my time. And they don't know it."
Jessica pressed her hands to her mouth.
Great Mother! He's the Kwisatz Haderach!
She felt exposed and naked before him, realizing then that he saw her with eyes from which little could be hidden. And that , she knew, was the basis of her fear.
"You're thinking I'm the Kwisatz Haderach," he said. "Put that out of your mind. I'm something unexpected."
I must get word out to one of the schools , she thought. The mating index may show what has happened .
"They won't learn about me until it's too late," he said.
She sought to divert him, lowered her hands and said: "We'll find a place among the Fremen?"
"The Fremen have a saying they credit to Shai-hulud, Old Father Eternity," he said. "They say: 'Be prepared to appreciate what you meet.' "
And he thought: Yes, mother mine—among the Fremen. You'll acquire the blue eyes and a callus beside your lovely nose from the filter tube to your stillsuit . . . and you'll bear my sister: St. Alia of the Knife .
"If you're not the Kwisatz Haderach," Jessica said, "what—"
"You couldn't possibly know," he said. "You won't believe it until you see it."
And he thought: I'm a seed .
He suddenly saw how fertile was the ground into which he had fallen, and with this realization, the terrible purpose filled him, creeping through the empty place within, threatening to choke him with grief.
He had seen two main branchings along the way ahead—in one he confronted an evil old Baron and said: "Hello, Grandfather." The thought of that path and what lay along it sickened him.
The other path held long patches of grey obscurity except for peaks of violence. He had seen a warrior religion there, a fire spreading across the universe with the Atreides green and black banner waving at the head of fanatic legions drunk on spice liquor. Gurney Halleck and a few others of his father's men—a pitiful few—were among them, all marked by the hawk symbol from the shrine of his father's skull.
"I can't go that way," he muttered. "That's what the old witches of your schools really want."
"I don't understand you, Paul," his mother said.
He remained silent, thinking like the seed he was, thinking with the race consciousness he had first experienced as terrible purpose. He found that he no longer could hate the Bene Gesserit or the Emperor or even the Harkonnens. They were all caught up in the need of their race to renew its scattered inheritance, to cross and mingle and infuse their bloodlines in a great new pooling of genes. And the race knew only one sure way for this—the ancient way, the tried and certain way that rolled over everything in its path: jihad.
Surely, I cannot choose that way , he thought.
But he saw again in his mind's eye the shrine of his father's skull and the violence with the green and black banner waving in its midst.
Jessica cleared her throat, worried by his silence. "Then . . . the Fremen will give us sanctuary?"
He looked up, staring across the green-lighted tent at the inbred, patrician lines of her face. "Yes," he said. "That's one of the ways." He nodded. "Yes. They'll call me . . . Muad'Dib, 'The One Who Points the Way.' Yes . . . that's what they'll call me."
And he closed his eyes, thinking: Now, my father, I can mourn you . And he felt the tears coursing down his cheeks.