Knowing v accepting

How do we draw the border between what we know and what we have learned from people who know?

The question is prompted by a discussion on a public post of Ed Brayton’s on Facebook about sophisticated theology and Karen Armstrong and agnosticism. Dan Linford (who teaches philosophy) said this:

Armstrong thinks that we can know that it is true that “God exists” but we cannot know what that sentence means, both because we do not know what God is nor do we know what ‘exists’ means.

I can’t make any sense of that. I can’t see what it can mean to know something if you don’t know its component parts. It seems like Dadaist gibberish to me. If I don’t know what ‘god’ is and I don’t know what ‘exist’ means, how can I know god exists?

It’s helpful in understanding mysticism, Dan said. Not to me it isn’t.

Dan drew analogies to a trusted friend telling you a sentence in a language you don’t understand is true, and thus you know it’s true, and to an instructor writing an equation that we don’t currently understand; we might trust the instructor that she is telling us true things.

But I wouldn’t say I know those things. That’s one place where I draw the border. I might accept it, but accepting something, taking someone else’s word for something, is not the same as knowing it yourself. It’s provisional. Knowledge is not provisional. If it is provisional, then it’s something short of knowledge. It may be good enough, it may be serviceable, it may be true – but for you it’s not knowledge.

Or am I all wrong?