At the risk of getting mashed up, I don’t think that understanding in this context admits of rational debate. There are experiences/emotions, such as love and maybe some aesthetic experiences, that are not really susceptible to discussion.

I think faith falls into that category. There is no suggestion that those who oppose the concept of faith are ‘ignorant’, simply that the world is perceived and experienced in a different way.

There is an irrationality in faith. I don’t think it can be discussed in the way that other beliefs, such as my support for the Irish Labour Party, can (though the latter probably verges on the irrational!). I would fully accept that religious belief and scientific belief are not analogous (as would the professor of geology in the church choir).

The point that was being made was that if you believed in whatever cause it was that was being supported by the writer of the graffiti, then you didn’t need any explanation of why and what you believed. If you didn’t believe in the cause, then no amount of explaining would be of any use.”

Your gloss and the original graffiti say different things.

I don’t agree with the graffiti. It doesn’t allow for the possibility that we can disagree with positions we understand – in effect, it claims you can only oppose something from ignorance, surely that ain’t right and it is to be deplored if it is. Ideally, if we don’t understand we should suspend judgement until we do and the explanation/justification/argument is to sway us one way or the other.

I have a professional obligation to disagree, too, with your gloss of the quote, which I take to enunciate the essential irrationality of belief; particularly where you say that if we don’t already believe something then we won’t be persuaded by any argument. If we won’t accept argument, what’s the point of the academy? what’s the point of the legal process? and why read reviews, heed advice or listen to anyone’s testimony? It’s an interesting question, though, if there are any sorts of belief (such as religious faith?) which do have an essentially irrational foundation. This would be a point of disanalogy from scientific belief, I think.