We all know the new series will revolve around the new Great Prophecy Rachel made in the end of The Last Olympian. Nobody can be sure what it means, but these are some theories and opinions about its meaning.

"Seven halfbloods should answer the call
The meaning of this line seems quite obvious. The problem is who are the seven halfbloods? The new characters we met in the sample chapters - Jason, Leo and Piper - are most likely to lead the group. Rick Riordan promised he wouldn't throw too many new characters at us, so we may meet some old characters from PJO, such as Thalia, Nico, Clarrise, Chris and Pollux, even some reborn demigods like Luck, Beckendorf, Silena, Ethan au Bianca and Annabeth's new friend Butch. Also, there maybe a satyr, a Cyclops, a clear-sighted mortal au a Hutress coming along, as there are some problems demigods can't handle themselves. Anyway, I think we can say for sure that R.R is focusing zaidi on the minor gods than in PJO.
We don't know much about the "call" either. It might be a call of the gods, a call for help from somebody who's in trouble au even a call from the "foes". It may also be a literal call, for example, a phone call au a horn call for meal.

"To storm au fire, the world should fall"
The meaning of this line is quite hard to guess. There are many theories about how and why the "world" would "fall". From the sample chapters, it's likely that Jason is "storm" and Leo is "fire". Besides, "storm" can also be Zeus, Poseidon, Typhoon, Aeolus and the anemoi thuellai. "Fire" can also be Hestia, Hephaestus and Prometheus. But how would "storm" au "fire" make the "world" fall? The most maarufu theory is that "storm" and "fire" will fight each other, and one of them will take over au destroy the world. The swali is what will turn them into sworn enemies? Will there be a sekunde Trojan War? What role will our 7 demigods play in that battle?
Some other people believe that the "world" is Gaea. In the myths, she was the creator of the world, and she took part in both Kronos vs Uranos and Olympians vs titans wars. She helped Kronos overthrow Uranos, but then got angry with her son for eating his own children. She decided to help Zeus fight the titans, but later she got mad at him too because he imprisoned Kronos and the other titans. People believe she will fall to "storm" au "fire" in the inayofuata series, perhaps she'll have to take a side au even fall in love.
Another theory is "storm" au "fire" will have to withstand Atlas' curse. "The world should fall" seems to describe exactly the feeling when wewe hold the sky. Other people think that the "world" may be the world in ancient myths (the Ancient Greek believed the world was flat). All of the theories above can be true, but whatever this line means, the word "or" must mean a choice, a choice that may affect the whole prophecy.

"An oath to keep with a final breath"
The first thing comes to mind when we read this line is that a person will swear something on river Stynx, but he/she will break it and die. However, the prophecy alisema "an oath to keep". That means the person won't break the oath but will die trying to keep it, so it isn't necessary to be on river Styx. Here's a orodha of some unfulfilled oaths and promises in PJO:
- Luke's promise to be Annabeth's new family. We all know Luke is trying for rebirth, and he'll be reborn again in a new form. What if he dies sabing Annabeth's life to keep his promise?
- Percy's promise to protect Bianca. Yes, Bianca is dead, but we don't know whether she's trying for rebirth au not. If she does, it's quite obvious that Percy will do anything to protect her.
- The Hunters' oaths to be loyal to Artemis and turn their backs to men. What would happen if a Hunter falls in love? Will she kill herself in order not to betray Artemis and her lover?
- Grover's promise to take care of the wild and wild animals. Bessie is still kept on Mount Olympus. If some evil forces try to kidnap him again, it will be Grover's responsibility to protect Bessie.
- The gods' oath to claim all their children kwa the time they're 13. We can't be sure if the gods will keep their oath au not. They are immortal, so they can get away with it very easily.
- Percy's promise to help Hermes' children. We all know Percy's fatal flaw. He would give up anything to save his friends!
So which of those oaths will end in a hero's final breath? au will it be a new one?

"And foes kubeba arms to the Door of Death"
This is the most important of the prophecy. As R.R confirmed, Kronos is now too weak to raise again. So who are the "foes"? We can be pretty sure that Dylan's "mistress" is involved. Then who is the "mistress"? Here are some opinions:
1-Gaea: Very possibly. Gaea is the creator of the world and the gods' grandmother, but she never got honor. Human are polluting the environment. Nobody is paying attention to her au her opinion. She has pretty good reasons to be unsatisfied with the current world and to want to build a new one.
2-Echidna, Typhoon's wife: Another good theory. Her husband Typhoon was captured kwa the gods in The Last Olympian, and she seems to be that kind of woman that will seek revenge.
3-Jason's stepmother: I'm not very sure about this. It's true that when a goddess is angry with her husband for going out with another woman, she can do plenty of dangerous things. Hera, for example, is known for taking revenge on Zeus' halfblood children. However, if it's really a jealous goddess standing behind this, how could her husband anger her so much that she wants to destroy the whole world?
4-A minor goddess: Minor gods don't have thrones on Olympus, don't have many temples, were never treated fairly and always have to do what the major gods told them to. That's why they easily chose to side with Kronos. However, like I mentioned before, R.R is obviously focusing zaidi on them in this series, so it's not likely they'll betray us again.
The inayofuata thing we need to find out is what the "Door of Death" is. It may be an entrance to Underworld. There're several of them: the regular one Percy used in TLT, the one Percy, Nico and Thalia used in The Sword of Hades and Orpheus' entrance. There's another theory that the Sword of Hades will be stolen again. That's a really good theory because the Sword can lock and unlock death, and it would be very dangerous if it falls into the wrong hands.

That's all we can guess for now. R.R refuses to give away any zaidi info, so all we can do now is wait until the book is out. Only 123 days left!