i think the last paragraph is something to do with yuna's pilgrimage

Not knowing the truth, yet fearing the past, --> she doesn't know that (SPOILER)there isn't a final aeon and worries about dying when beating sin, as other summoners have in the past
Yet you you prevail, the trio will help, --> she defeats sin and Yu yevon
But beware, though the enemies death comes fast, --> yu yevon is surprisingly easy to kill, as are (SPOILER) you aeons after theyve been transformed, most likely because of constant auto-life
But the strong become weak, just like that little whelp. --> the strong aeons that fought beside you become weak enemies, and with each one you kill, the "little whelp" (yu yevon) becomes weaker too.