I don't think it's to share but to complete the prophecy.
I think in the show Danaerys only rides one of the dragons. That is likely more foreshadowing based on the book's theory of the 3 headed dragon. Now when they say the 3 headed dragon lets assume that they are talking about 3 dragon rides here to take back Westeros in all its glory as opposed to 1 person being the 3 headed dragon (which is what I think you are saying. ) The 3 headed dragon on the black background is the seal of House Targaryen and I believe for the true return of the house, you will need all 3 heads.. In this case... they are Daenarys, Jon, and none other than Tyrion Lannister..
Daenarys Targaryen
No explanation needed. Her mom died during child birth.
Jon Snow
Assuming R+L=J is true which we can based on how things are proceeding, he is actually the love child of Rhaegar Targaryen and Lyanna Stark who died during childbirth that Ned Stark adopted to keep the honor of his family name.
Tyrion
- Tywin Lannister isn't Tyrion’s real father. The Mad King raped Jaime, and Cersei’s mother who died during childbirth and he is therefore Tyrion’s biological father. That’s why Tywin constantly insisted he was “no son of mine.” Also Tyrion wasn't burned to bits when he freed the dragons,
The Parallels Between Tyrion, Jon, and Dany make me think that they are for sure the 3 headed dragon symbolizing the return of House Targaryen.... now when it comes to the mythical heroes that gets a little trickier.
If you look at the theories of old, there is the hero stories about Azor Ahai, The Prince that was Promised, and the Last Hero, Now we've pretty much assumed, these are different cultural explanations of the same person but I disagree. I'm starting to think that it's 3 different people each playing their part to bring back the 1 mythical person similar to a 3 headed dragon.
So you have 3 ancient figures..
So lets start looking at these characters
The Prince that was Promised - Religion: R'hllor/Valyrian Myth
At the end of book 5 Master Aemon is quoted as saying this to Sam as he lay dying
"No one ever looked for a girl..It was a prince that was promised, not a princess. Rhaegar I thought … the smoke was from the fire that devoured Summerhall on the day of his birth, the salt from the tears shed for those who died. He shared my belief when he was young, but later he became persuaded that it was his own son who fulfilled the prophecy, for a comet had been seen above King’s Landing on the night Aegon was conceived, and Rhaegar Targaryen was certain the bleeding star had to be a comet. What fools we were, who thought ourselves so wise! The error crept in from the translation. Dragons are neither male nor female, Barth saw the truth of that, but now one and now the other, as changeable as flame. The language misled us all for a thousand years. Daenerys is the one, born amidst salt and smoke. The dragons prove it."
This quote goes on to say that in High Valyrian, the word Prince has a gender-neutral meaning to it.
Azor Ahai - Religion:
R'hllor
"
According to prophecy, our champion will be reborn to wakedragons from stone and reforge the great sword Lightbringer that defeated the darkness those thousands of years ago. If the old tales are true, a terrible weapon forged with a loving wife's heart. Part of me thinks man was well rid of it, but great power requires great sacrifice. That much at least the Lord of Light is clear on."
―
Thoros of Myr[src]
"I pray for a glimpse of Azor Ahai, and R'hllor shows me only Snow." - Mellisandre
Also in A Dance With Dragons, Jon Snow had this dream
"Burning shafts hissed upward, trailing tongues of fire. Scarecrow brothers tumbled down, black cloaks ablaze. "Snow," an eagle cried, as foemen scuttled up the ice like spiders. Jon was armored in black ice, but his blade burned red in his fist. As the dead men reached the top of the Wall he sent them down to die again. He slew a greybeard and a beardless boy, a giant, a gaunt man with filed teeth, a girl with thick red hair. Too late he recognized Ygritte. She was gone as quick as she’d appeared."
Reborn... Terrible weapon forged with a loving wife's heart....great sacrifice.
Last Hero - Religion: First Men
As told by old Nan to Bran
"Now these were the days before the Andals came, and long before the women fled across the narrow sea from the cities of the Rhoyne, and the hundred kingdoms of those times were the kingdoms of the First Men, who had taken those lands from the children of the forest. Yet here and there in the fastness of the woods, the children still lived in their wooden cities and hollow hills, and the faces in the trees kept watch. So as cold and death filled the earth, the last hero determined to seek out the children, in the hopes that their ancient magics could win back what the armies of men had lost. He set out into the dead lands with a sword, a horse, a dog and a dozen companions. For years he searches until he despaired of ever finding the children of the forest in their secret cities. One by one his friends died, and his horse, and finally even his dog, and his sword froze so hard the blade snapped when he tried to use it. And the Others smelled the hot blood in him and came silent on his trail, stalking him with packs of pale white spiders big as hounds –"
If you ask me, this points to Daenarys, Jon, and Bran...
and so it would appear that all 3 have to find each other to defeat the white walkers once and for all and restore peace to Westeros.