[RexNorton]

In the first scene of the game, we see Aeris' head facing straight at us, her eyes already open (life). When Sephiroth draws his sword from her body we see her eyes close (death). In the final scene we see Aeris' head nodding upward and her eyes opening (returning to the Planet or resurrection).
We have already established that many major truths in this game are illustrated in the places where we are least likely to notice them. The most fundamentally absurd scene in the game is the show at the Gold Saucer during Aeris and Cloud's date. The scene is so goofy that we are totally encouraged to play it as mischievously as possible (another way the game diverts us from its truths).
Let's look at the entire scene through the path to the happy ending. I will add what I think to be the secret references to the story and what they mean in brackets.

Narrator:
Long, long ago... An evil shadow appeared over the peaceful kingdom of Galdia...
[Jenova, "the winged one of the lower reaches," who started reaping her destruction upon the planet 30 years before the game begins]
Princess Rosa was just kidnapped by the Evil Dragon King Valvados.
[Aeris was killed by Sephiroth/Jenova]
What will become of her?
[What is Aeris' true fate?]
Just then, the legendary hero, Alfred, appears!!
Knight:
"Oh...... you must be the legendary hero... Alfred! Hey, it's your line.
[It's your decision to make]
Yeah, you. Ahem! Oh, you must be the legendary hero... Alfred! By my soul, please... please save Princess Rosa
[In your soul you can save Aeris]
Now... please talk... to the King!!
King:
Oh... legendary hero, Aldred. You have come to save my beloved Rosa...
On the peak of a dangerous mountain...dwells the Evil Dragon King, Valvados...
[In the Northern Crater dwells Jenova. Note that both Jenova and Valvados have three syllables in their names]
who's kidnapped Princess Rosa...
[who has killed Aeris]
But... you can't beat the Evil Dragon King now!
[Cloud is still too confused about himself to fight Jenova]
Talk to one who can help you...
[talk to Tifa Lockheart, who holds 'locked' within her 'heart,' the key to Clouds true past]
Cloud has two choices:
1. The knight (a symbol of force)
2. The wizard (a symbol for wisdom)
Let's have Cloud choose the wizard.
Wizard:
I am the great wizard, Vorman.
[I am truth]
What do you wish to know?
Cloud:
The Evil Dragon King's weakness
[Jenova's weakness]
Vorman:
Ahh, the weakness of the Evil Dragon King. It must be, it must be... Yes, it must be... True Love [Truth and Love]! The power of love... Is the only weapon that can withstand the fangs of the Evil Dragon King...!
[Only love can save Aeris from death]
Oh what is going to happen next?
[Only Cloud can decide Aeris' fate]
Oh... legendary hero... look!
EDK:
Gaaaaaaaah! I am the Evil Dragon King.... Valvados!
[I am Jenova]
I have not harmed the Princess...
[Aeris is being contained inside Holy, which has been sealed]
I have been expecting... you!
Aeris:
Please help me... legendary hero!
[Please save me from Jenova, Cloud!]
How was that?
EDK:
Gaaaaaah! Here I come, legendary hero... Alfred! I already know... your name!
[I have been controlling you all along]
Vorman:
And now... legendary hero... Here is what will happen... to your beloved... A kiss! The power of True Love!!
[Aeris will return through Clouds love]
Aeris:
Cloud... I mean, Alfred...
Evil Dragon King:
Arrggaahhh! Curses... The power of... love!!
King:
Oh... behold! Love has... triumphed!
[Cloud's love has brought back Aeris]
Now let's all return... and celebrate.
Yes let's... yes let's... !
Narrator:
Oh, how profound the power of love...
[profound means 'within,' Holy is contained at the center of the planet]
And so the legendary hero Alfred and our story live on happily ever after.
[Cloud defeats Jenova and Sephiroth and finds Aeris in the Promised Land]


If you choose Tifa over Aeris, it breaks the points of focus that symbolize Aeris and the Triangle of Manifestation. I think that Aeris' resurrection is determined by whom Cloud chooses in the love triangle. If Cloud chooses Aeris, he completes the Triangle of Manifestation and brings Aeris back, through the power of love, when he is touched by Holy (Note that Aeris hand appears immediately after Cloud is touched by Holy and this scene immediately shifts to a shot of Tifa's hand reaching towards Cloud). If he chooses Tifa, Aeris goes back into the Lifestream. After all, any good RPG will often let you decide something fundamental to the fate of your protagonist.
Remember what Aeris says about the Promised Land, "You don't 'know' where the Promised Land of the Ancients is. You search and travel until you feel it. Like you just know, '... this is the Promised Land.'"
The Promised Land is not a place, but something you find in your heart. When Cloud is snapped back into reality at the end of the game, he says to Tifa, "I think I'm beginning to understand. An answer from the planet... The Promised Land... I think I can meet her there." Cloud somehow knows that he can bring Aeris back by keeping her alive in his heart. If Cloud loves Aeris then she is his Promised Land, thus providing the explanation for her resurrection when Cloud is touched by Holy. But Aeris loves Cloud no matter how he feels.
If Cloud chooses Tifa over her, then she has no real reason to come back. She is better off in the Lifestream with her own race. This resurrection/Lifestream return riddle is somewhat ambiguous. But, when you understand the mythological references in the game, the choice between Aeris and Tifa steers it to a more likely possibility, which is why I think this determines Aeris' fate.
I think Square put this riddle in the game as a sort of 'reward' for people who take the time to read about the mythology on which the game is based. They wanted to encode something in the game, which could only be understood by understanding the most subtle levels of the game. I can really see why Square of Japan translated FFVII themselves. There were just way too many symbolic elements encoded into the game for them to risk it all being ruined by having someone else translate it.
FFVII touches a level of depth in both its dramatic story telling and in its symbolism that has never been approached by another RPG. I've never played a video game which has challenged me more in it's requirement of the player to think about it's story in order to understand it. This is a very confusing story and I hope that I've done a good job of explaining the tale and its intriguing mythological basis.
If I've done my job right, then may this FAQ serve as an affirmation of appreciation that inspires the many FFVII fans to play the game once again, with new eyes...