En Sabah Nur, the big blue bad guy with a taste for destruction, and supposedly the world's most ancient and powerful mutant, does a lot of talking in [X-Men: Apocalypse](tag:1194267). He talks about how mutants "follow blind leaders". He promises to "build a better world" from the ashes of all that destruction he thrives on.
Although at surface level Apocalypse is an entirely one-dimensional villain and the least entertaining aspect of the movie, there's actually quite an interesting discussion to be had about what's driving him. Is he insane, evil, or simply so arrogant that he's hell-bent on erasing the world he had no part in building in order to make his own, superior influence felt? He disparages those who follow blind leaders, but the Four Horsemen he assembles begin blindly following him. Maybe irony just wasn't a thing six thousand years ago.
There's also a very solid argument to be made that I've already considered this more than anyone who actually wrote or created this movie. So, while I could and probably will dive deeper into the psychology behind Apocalypse at some point (even if in vain), let's instead focus on the one line of dialogue Oscar Isaac's supervillain speaks that has both crystal-clear intent and major consequences for the future of the X-Men franchise.
During the movie's wildly dramatic climax, a fight scene between Xavier's students and Apocalypse's Horsemen which manifests as a complete sensory overload, Jean Grey unleashes the Phoenix Force that's been hidden somewhere inside of her. It's a turning point for Jean and Charles, his plea for her to unlock her full potential representing a major change of heart on his fundamental belief that powers should be controlled. To defeat Apocalypse, Jean must truly let go. And so she does. And it's everything.
But as En Sabah Nur crumbles to dust, amid a crescendo of noise so loud you could almost miss them, those three words are spoken in a way that feels unmistakably like a prophecy. So what did Apocalypse actually mean?
In Marvel Comics lore, the Phoenix is not just something that allows Jean Grey to walk on air and overpower a mutant like Apocalypse: it's literally the most powerful cosmic force in the galaxy. Not only immortal and impossible to destroy, the Phoenix serves one specific purpose: to burn anything and everything that doesn't comply with the forward nature of life. To rid the universe of unnecessary parts. To ensure constant evolution.
Anything that doesn't fit the bill will unleash the wrath of the Phoenix force, at which point Dark Phoenix comes into play. And that's when the universe needs to start watching its back.
Unless you successfully found a way to forget (in which case what's your secret?), you'll probably be familiar with the unholy mess The Last Stand made of the Dark Phoenix Saga. Bryan Singer even has Jean herself taking shots at it here with a deliciously shady remark about how the third in the trilogy is always the worst.
Those words spoken by Apocalypse seem to suggest that he saw something in Jean Grey in that moment which alerted him to the cosmic entity inside of her, something Xavier and the X-Men don't seem to be fully aware of, or at least don't recognise the full potential of. Could it be that by encouraging Jean to awaken the Phoenix inside of her, Charles inadvertently set something into motion that will manifest as the Dark Phoenix sometime in the near future? The Professor being responsible for that would be a darkly ironic twist considering his entire life is devoted to helping his students recognize and control their mutations.
It's also entirely possible that the Phoenix's existence within her binds Jean Grey to the Dark Phoenix and the destruction that comes with it, and that Charles merely accelerated the process. Even early on in the film, Jean's nightmare at the X-Mansion and the feeling she describes as coming from within her, growing stronger "like a fire" feels clearly like a dark vision of the future cataclysm caused by Dark Phoenix as opposed to the imminent rise of Apocalypse.
To take that theory one step further, even the title of the movie could be interpreted as a foreshadowing of everything that's still to come in Jean's future, rather than just a reference to some slightly demented bad guy from the pyramids. That theory is lent added credence by the fact that En Sabah Nur is never once referred to as Apocalypse and, as one MoviePilot creator smartly observed, the most famous piece of apocalyptic literature is the Bible's Book of Revelation.
Ultimately, X-Men: Apocalypse is all about revelation. The power at the core of Jean Grey, the infinite potential for absolute ruination of everything known to man, is revealed — and nobody truly realizes it.
But we do.