We know that prophecies exist in Harry’s world. All of the prophecies that affect Harry in some way eventually come to pass. The wording is always ambiguous enough to cause anxiety, though. “The one with the power to vanquish the Dark Lord” meets these particular characteristics and will either kill Voldemort or die trying… or kind of both. Voldemort’s “servant has been chained these twelve years” and will soon rejoin his master, but—plot twist—the servant isn’t the prisoner for whom the book is named. “When unseen children murder their fathers, then will the Dark Lord return”—but maybe not, erm, permanently.
If Firenze is to be believed, occupants of the Wizarding World have some free will—but the “great tides of evil or change” will come and go more or less as the heavens foretell. The ambiguity of the Prophecies we encounter in the series seems to act as a catalyst for these “great tides of evil or change.” It seems to me that the anxiety provoked by these prophecies usually favors the non-evil. Voldemort tries to kill Harry and is put out of commission for 13 years as a result of hearing part of the prophecy. Harry seeks and destroys Voldemort’s horcruxes as a result of his call to responsibility. Harry doesn’t really have time to respond to the “servant and master” prophecy before it comes true, but it adds credibility to her earlier prophecy, which calls him “…the one with the power to vanquish the Dark Lord.” We don’t know exactly when or how Delphi stumbles upon the prophecy in Cursed Child, but we know that she and Scorpius argue about whether or not prophecies can be broken, and that finding the prophecy is what clues Harry and co. in on what is happening with Albus and Scorpius. We can safely assume that Delphi approaches Albus because she thinks he will lead her to a Time-Turner—Mr. Diggory suspected Harry had one. Once Scorpius convinces Delphi that prophecies can be broken, she takes them back in time to prevent “the big one”—the moment Voldemort marks Harry as his equal.
I wonder sometimes what the point of a prophecy is, if it is inevitable. I think Scorpius is putting his best Slytherin foot forward when he convinces Delphi that they can be broken—if she had continued on her quest to “spare the spare” and enable the new prophecy, it is hard to say what might have happened. I think the means by which a prophecy comes to pass is flexible—especially if there is a Time Turner lying around. But I think the prophecy itself may be some kind of gift to counteract evil forces. Perhaps that is why only some witches and wizards have “the Sight,” as Professor Trelawney would say. Maybe it’s like Dumbledore’s protection of the Sorcerer’s Stone—only those who wish to find it, but not use it, are able to get it. Perhaps the Sight is a gift for those who are essentially good at heart, but effectively pretty neutral. But I think all of that is a concept for another Minute, so I’ll wrap this one up.