And just to clarify that the Bene Gesserit plant myths all over as part of the Missionaria Protectiva to help their own in any time of need, something Jessica plays along with not because she believes Paul is the fulfillment of the Fremen prophecy, but because she recognizes that they will need Fremen help to survive Arrakis, and so uses this prophecy to manipulate them. This is underlined in the film by Zendaya's character who openly says as such.You're going against the text all the time.
I'm re-reading Dune at the moment and the chapter where Jessica first meets Shadout Mapes on Arrakis implicitly describes this as well, from the introduction to the actual dialogue. I'll include a few quotes from the text below to help you understand this better:
With the Lady Jessica and Arrakis, the Bene Gesserit system of sowing implant-legends through the Missionaria Protectiva came to its full fruition. The wisdom of seeding the known universe with a prophecy pattern for the protection of B.G. personnel has long been appreciated, but never have we seen a condition-ut-extremis with more ideal mating of person and preparation.
‘The Fremen have learned that you’re Bene Gesserit,’ he said. ‘There are legends here about the Bene Gesserit.’
The Missionaria Protectiva, Jessica thought. No place escapes them.
‘My husband told me of your title, Shadout,’ Jessica said. ‘I recognized the word. It’s a very ancient word.’
‘You know the ancient tongues then?’ Mapes asked, and she waited with an odd intensity.
‘Tongues are the Bene Gesserit’s first learning,’ Jessica said. ‘I know the Bhotani Jib and the Chakobsa, all the hunting languages.’
Mapes nodded. ‘Just as the legend says.’
And Jessica wondered: Why do I play out this sham? But the Bene Gesserit ways were devious and compelling.
‘Do you know this, my Lady?’ Mapes asked.
It could only be one thing, Jessica knew, the fabled crysknife of Arrakis, the blade that had never been taken off the planet, and was known only by rumor and wild gossip. ‘It’s a crysknife,’ she said.
‘Say it not lightly,’ Mapes said. ‘Do you know its meaning?’
And Jessica thought: There was an edge to that question. Here’s the reason this Fremen has taken service with me, to ask that one question. My answer could precipitate violence or … what? She seeks an answer from me: the meaning of a knife. She’s called the Shadout in the Chakobsa tongue. Knife, that’s ‘Death Maker’ in Chakobsa. She’s getting restive. I must answer now. Delay is as dangerous as the wrong answer. Jessica said: ‘It’s a maker—’
‘Eighe-e-e-e-e-e!’ Mapes wailed. It was a sound of grief and elation. She trembled so hard the knife blade sent glittering shards of reflection shooting around the room.
Jessica waited, poised. She had intended to say the knife was a maker of death and then add the ancient word, but every sense warned her now, all the deep training of alertness that exposed meaning in the most casual muscle twitch. The key word was … maker. Maker? Maker.
Still, Mapes held the knife as though ready to use it. Jessica said: ‘Did you think that I, knowing the mysteries of the Great Mother, would not know the Maker?’
Mapes lowered the knife. ‘My Lady, when one has lived with prophecy for so long, the moment of revelation is a shock.’
Jessica thought about the prophecy – the Shari-a and all the panoplia propheticus, a Bene Gesserit of the Missionaria Protectiva dropped here long centuries ago – long dead, no doubt, but her purpose accomplished: the protective legends implanted in these people against the day of a Bene Gesserit’s need. Well, that day had come.