It also follows the themes of a lot of old Greek plays - how fate is inescapable, and you have to accept it to know peace. Just as Misia was satisfied with her life, unlike how Elef struggled and suffered to the very end. And it's got a lot of the same irony as, say, Oedipus, in that a dark prophecy was told of a royal birth, and the royal family tried to avoid it by sending their child away, only to have everything play just as destiny dictated.
Those kinds of stories are meant to be cathartic in their sorrowful nature, but I've always just kind of been disappointed by them. When the message of a story is presented like you can't change your fate, and that your own story is not something within your control and is instead in the hands of some distant god, it's all just a huge downer to think about. It begs questions like, does free will truly exist? I gotta say, I'm not a fan of those kinds of questions.
Which isn't to say that Moira disappoints me, of course. And it also doesn't mean that this is the only message to be taken away from Moira. It's just a connection with related tragedies that's worth noting, I guess.