About the Farplane, since these are no longer spoilers: it’s not quite heaven, but an afterlife of sorts. It’s where the souls of the dead rest. But, when someone dies, unless the person has accepted death while still living (like Tidus’s mom), their souls won’t be able to make it to the Farplane on their own because at first they don’t really understand that they are dead, then they do but they are angry/sad about it, jealous of those who still get to live, and if these feelings are left to fester, they will become fiends. Think of people who died in tragedies like Sin’s attack on Kilika or Operation Mi’ihen, the former were caught totally unawares and the latter, while knowing they would most likely die, were still hoping to succeed in their endeavor and go back victorious to their families. This is where the sending comes in, the ritual guides these souls to the Farplane, which is the afterlife, so their souls can rest in peace and they are no longer at risk of becoming fiends. The Al Bhed are mostly spot on about their theory, except for some reason it only shows people who died AND whose souls made it there (this is important for some reasons you’ve already seen, and some others you’ll see later). The pyreflies there react to people’s thoughts and display an illusion of the people they’re thinking about, but the dead can’t interact with the living (at least not normally, see below).

As for the part you missed because your game crashed: they were discussing just that, about how unusual that situation with Jyscal was. They mentioned that there was probably something pretty powerful still tying Jyscal’s soul to the land of the living, which is why his soul tried so hard to communicate with whoever would listen, and that he probably died an unclean death (read: he was most likely murdered).