Jon Snow and Daenerys Targaryen are two of the most beloved characters in Game Of Thrones (fans have the tattoos to prove their love). They've risen as the two primary protagonists of the show. They also seem to be the best equipped to fight the true big bads of the series.
Yes, we all hate Cersei, Littlefinger, Ramsay and Joffrey. But they are minor threats compared to the White Walkers. These creatures form no alliances and aren't interested in politics. They want to kill everyone.
So far, we've only seen the White Walkers expose a weakness to one of two weapons. One is Valyrian steel. This is an extraordinarily rare metal. Jon Snow's sword, Longclaw, is one of the few weapons made of this White-Walker-killing material.
We've also seen this dagger that was initially used to try and kill Bran Stark, but now is in the hands of Arya (will we see her kill some White Walkers? We can only hope). Dragonglass is the other material strong against the icy villains, and mining this is what brought Jon Snow to meet Daenerys.
You have to ask yourself, why don't they seek out more Valyrian steel as well? Surely steel is better than glass, right? The problem is Valyrian steel is only found in Valyria, and you may remember the issue with traveling to Valyria.
Valyria is crawling with Stone Men. These are people afflicted with greyscale, a disease that causes your skin to grow thick scales and turn into a mindless zombie. But not like the literal zombies the White Walkers create. This show is full of zombies.
Jorah is a disgraced knight. He was exiled after partaking in slaving. He did this to try to earn money for his wife, who ultimately left him for a richer man. He was at one point also exiled by Dany when she learned he sold information about her to Varys ("The Spider").
That man? Jorah's father, former Commander of the Night's Watch, Jeor Mormont. Jeor was also the man who gave Jon Snow Longclaw, a weapon he's used to kill White Walkers and learn that was a weakness of theirs to begin with. It's only fitting his son could be the man to help save everyone.
Now that Jorah's been cured of greyscale, many theorize he may have an immunity to it. This means he can return to Valyria and gather more Valyrian steel to use in the upcoming war with the White Walkers. It would be a dangerous mission, but one he's capable of and would be willing to undertake.
Jorah Mormont committed atrocities. But if he is able to play an instrumental role in saving thousands of lives, he just may redeem himself. Weirder things have happened, in fiction and even in real life.