There is truth about God. I assume that I know what that truth is. But that doesn't mean I can assume that those who do not agree with me are deceived, stupid, or willfully ignorant. I can be confident that I am right. Not to be confident is not to be a believer. But I ought not to be proud in my knowledge and belief.
Being proud in interfaith discussion means assuming that I've explained myself sufficiently well. It means failing to recognize the integrity of others' beliefs and the sincerity of their faith. It means entering into the discussion as if I am there only to instruct the other person and not to learn. Indeed, it means assuming that the other person doesn't have something to teach me.
Even if, perhaps especially if, another person's beliefs are quite different than mine, even if I am confident that she is wrong and I am right, I ought to assume that she is thoughtful, reasonable, and well-informed. And whatever our reasons for talking together, I ought to listen for what I can learn. I ought not only to leave room for what Krister Stendahl called "holy envy," I ought to strive for it. Knowledge and holy envy are complementary rather than antithetical, but pride and religious knowledge are antithetical.