Zio Mc on Nostr: I'm reading your note just now and it looks you know a lot about encryption, nostr ...

I'm reading your note just now and it looks you know a lot about encryption, nostr and nips.
I've got a question about nip59, why i need to use the content of the message inside another event called rumor and not directly in the seal?
And is not clear how can i decrypt a gift wrapped once sent, do i need to store the privkey of the ephemeral generated key?
Thanks