[quote]He prompted Spark to explain the rings' true nature, as though he knew and believed it himself.[/quote]No, he didn't truly know for sure yet. He was asking Guilty Spark to know for sure. And when he gets his answer, you can hear him choking back the tears (or the Sangheili equivalent) when he says, "Tartarus," which he quickly turns to anger, "the Prophets have betrayed us." As for the main question of the thread, I can't really say unfortunately. I think it might have to do with the Gravemind knowing the Great Schism going on, so it was going to shake up his faith. And then there's that part that where he has the flashback of what the Gravemind said. So I don't think it was "show you" in the literal sense, but more that, "Hey, if you won't believe me, you'll find out through circumstance." Hope that makes it make more sense.