So, Jephtha: he was an Old-Testament guy who was banished by his family on account of being illegitimate. But when they need someone to help them defeat the Ammonites, they bring him back and agree to make him their king.
So he goes, but before that, he makes the great decision to promise that if he's able to win, he'll murder the first person he meets, as tribute to God. Um. But then he sees his daughter, doh! He's not happy with it, but he goes ahead and murders her 'cause whatteryagonnado?
Here's my question: what if it HADN'T been his daughter? What if it had just been some stranger? Would his reaction have been to cheerfully go, welp, better slaughter this person because I told God I would!" That kind of behavior nets you multiple life sentences in this day and age. To be fair, unlike with Abraham and Isaac, there's no actual indication that God really wants him to be doing this--it's just his own personal madness. But if God objects to this, he's sure quiet about it.
I mean, I know pointing out how fucked up some Bible stories are is kind of hacky, but it's hard not to when faced with this. But it's still a problem: they may be interesting illustrations of primitive religion, but when you're asked to take the drama seriously--well, it's hard.
So people have long been uncomfortable with this story, it seems. If you look at the text, it seems pretty clear. Some have argued that, no, she was just, like, secluded and dedicated to God for the rest of her life, but I really feel like you'd have to have a vested interest in the story being other than what it is to make that argument. Not that this really makes it that much better. But it IS what this oratorio does. God sends an angel to tell them, no no. Sure, better than dying, but damn, man--she has a fiance! She's looking forward to getting married! And now, all of a sudden, sorry, nope, we're completely derailing your entire life because of this incomprehensible cosmic wheeling and dealing that's going on around us. They both seem quite chirpy about it--at least in this production--but you know they are just SEETHING inside. My head-canon is that they emark on a long, secret affair, in defiance of all this arbitrary theological gibberish.
In any case, either way, it's just this cruel, ridiculous story, and you sort of wish Handel could've found a better libretto. AND YET! Well, it is Handel, and this is his final oratorio, meaning his final dramatic work of any kind. I'm not going to sit here and tell you that I'm enough of a Handel expert that I can distinguish between his early and late work, so I can't say "ah ha, you can see how ideas he had been working on for many years finally come to fruition here." But GODDAMN this is great music. What's more, lot of the arias work dramatically in and of themselves, as long as you don't think about the larger context, and I'll go even further than that: there are parts where you're so carried away that you don't care about the dubiousness of the story; you're so swept up that you have to just go with it. And that is my ultimate piece of praise for this piece (wha?!?).