It's an opera. Die Walküre. First performed in 1870 I now discover, although it was written somewhat earlier. (Big row between the composer and mad King Ludwig about performing rights. Ludwig eventually pulled rank and won.)
The question of divine punishment is really, really interesting. The twins are the children of Wotan (Odin), head god, but count as human because of their human mother. Except they're also werewolves but maybe don't go there. Love has been cursed at an earlier stage of the drama, I believe banished from the cosmos, leaving Freyr (Froh) and Freyja (Freia) empty husks. (He's an airhead and she's a cardboard cut-out who does nothing but scream.)
The male twin (Siegmund) has been bred by Wotan to be the Free Hero he believes is needed to regain the cursed ring of power, and the female twin (Sieglinde) seems just to have happened. They are separated as children, Wotan's doing so he can bring the boy up himself by training him in misfortune. The girl is trafficked into a forced marriage. They meet again as young adults without immediately recognising each other and fall so comprehensively in love that there really is a feeling of something supernatural behind it. Here's the rub. They recognise their relationship before the sex scene and carry right on regardless.
There is an extraordinarily telling scene during the recognition process which is always dismissed as a let's-hold-up-the-drama-for-a-love-song interlude, but which I think is crucially important. The door flies open, the moon (masculine in German) floods into the room, and everything is transformed. Siegmund (who doesn't admit to having realised that this woman is his sister until considerably later) sings about Spring (also masculine) breaking down the doors of winter to rescue his sister, Love (feminine), and making her his bride. Sieglinde immediately respondes with "Du bist der Lenz" (You are the spring), sung to the part of Freia's original motif that has become the twins' love motif but which I think carries the broader connotation of love as divinity. There's more, but whatever.
Anyway, next act, Wotan's wife Fricka (Frigg), goddess of marriage among other things is doing her nut because Sieglinde's husband has prayed to her for vengeance against the adulterer (he doesn't know that it's incest too, but Fricka certainly does - Blutschande in German). She demands that Siegmund must die as a punishment. Wotan is having none of that and never agrees, but he changes the subject to explain that Siegmund is the necessary free hero who will recover the ring and save the gods from the curse. It takes Fricka less than five minutes to demolish that one, how can he be free from the influence of the gods when Wotan fathered him and brought him up and trained him? It's cheating. Wotan is crushed and realises that he has to kill Siegmund.
Except he sends his favourite valkyrie daughter to do the deed, and she is so overcome with compassion for Siegmund that she disobeys her father and that is the major turning point in the drama. (She in fact becomes the eventual free hero because of her rebellion - she who was Wotan's will has turned against his will to do the deed he himself was forbidden to do, but he never realises this because he thinks the free hero has to be male, and that goes for most of the audience too, at least until relatively recently.)
Siegmund does indeed die, because Wotan is so incensed by his daughter's rebellion that he intervenes, and so does Sieglinde, but later, in childbirth. So is this divine punishment for incest? Some commentators think so, but I disagree. Wotan doesn't believe that what those two did was wrong. He actually kills Siegmund because he has realised he was deceiving himself with the plan to rear and groom a so-called free hero, and is so furious with himself he takes it out on the twins.
Another paradox is that we're constantly being told that Siegmund is no more than a clone of Wotan, practically a mindless construct, so how can he be free? Both Fricka and Wotan take that line. But in fact Siegmund as a person is about as different from Wotan (who is an absolute bastard at this point in the drama) as it is possible to be. I've never seen this discussed.
Anyway, I'll bet you're sorry you asked now. I was just working on it when I took a quick break to listen to your video and the incest reference struck me. This is what happens when you spend years reading scholarly tomes about the greatest work of art in western literature and find yourself violently disagreeing with pretty much all of them.