What did the Gravemind tell John & Arbiter?

In Halo 2, during the cutscene in which the Gravemind speaks to John and the Arbiter, he tells them (near the end) “…if you will not hear the truth, then I will show it to you.”
What do you think he told them? Obviously, he could have told them anything, including the history of Precursors and Forerunners. However, I am more inclined to think that he told them only what they needed to hear in order to be convinced that he was telling the truth. Whatever it was, it was effective enough to change the Arbiter’s mind to the point that he abandoned a core tenet of his religion and did the bidding of a “parasite.”
Any ideas?

I think since we’re going as far back(?) as Halo 2, the Gravemind was acknowledging the Covenant’s delusion regarding Halo’s purpose.

It is a super weapon, yes yes, but the Covenant viewed them as a gateway of sorts.

We hear exactly what he tells them in the cutscene. I mean… honestly, what made you think there was more to it than that?

yea cuz the arbiter still didnt believe the truth behind the halos and the great journey