The Revelation campaign is the third and final campaign in the game. It's highly recommended that you finish both of the other campaigns first to get the most out of it and I can see why. Revelation pulls from both of the other stories and gives you the details about what's happening behind the scenes. It's the middle path, and the one I think I would have chosen if given the option initially.
It's super cool to see all these main characters that had to fight and kill each other in the other two campaigns finally meet as allies. It allows for all sorts of interesting conversations. Pairing up troops from opposite sides of the war was especially fun.
Not to mention that the ending of this campaign felt like the true ending of the game. Both of the others were satisfying but incomplete. Playing through all three campaigns feels like the true way to experience the full game.
Having finished off Fire Emblems Fates now I'm excited to see what the mobile version of Fire Emblem will have to offer on smart phone this fall.