No, this is not a post about a vision-impaired Pope*, although that in itself might make an awesome post. This post is instead about blindness, and how there are none so blind as he who would not see.
Now, there are all kinds of congenital conditions of blindness, and for the purposes of this thought experiment, I want to pick one where the entire optical pathway does not exist. At least, insofar as the eyes as well as the optic nerves are missing from a man's physical makeup. Here's the experiment; how do you explain sight to such a man? In a way he will truly understand?
This is a serious question, and one I can find no answer for. We take sight so much for granted - indeed, of the world's 6-billion-plus people, approximately 50 million are totally blind (well, have been found to be, at any rate, the true number may be more, let's say double), and of that figure, ~12% are congenitally so - we would be hard-pressed to explain it to someone who has never experienced light. Let me put it this way. 12 million people out of 6,000 million is 0.2%. Now, remember (or be enlightened, heh heh) that sighted people receive 70-80% of information concerning their surroundings from vision. Hence, 99.8% of us rely on (or have at some point relied on) light and sight to give us 80% of the information we use to be situationally aware.
So go on. Such an overwhelming majority of people surely should be able to answer this question as posed on Yahoo! Answers, right**? But do you know what the best answer was, as rated by viewers? "You can't." I like the further response here...
I would wouldn't bother to attempt to describe something that the blind have no concept of. They would have their own map of the world using their remaining senses, such as sound and touch.
Now, you gotta figure, vision is crucial to sighted humans. I would go so far as to say that it is fundamental to everything we do. The slightest impairment of our vision can have a devastating impact if we're not careful. But none of us can explain something so simple, so obvious, so... ubiquitous, to someone who has no concept of it.
Let me go further. How do you describe red-hot chilli peppers to someone who literally cannot see red i.e. someone with protanopia (red-green colour blindness)? You can't, because they don't have the referents.
So, I hope this has got your brains spinning. Because the last series of questions I want to pose on this topic is taking this issue, and turning it entirely around. On what basis should a congenitally blind man, lacking eyes and optic nerves, believe any of us when we speak of the concepts of light and vision? What is he to make of us when we speak of light as both wave and particle? What meaning would the double-slit experiment have for him? And of what particular use would light be to a blind man?
Why these questions? Well, I thought it'd be apparent to anyone by now where I'm going. But just to clarify, I am speaking of spiritual blindness. I don't even want to talk about adherents of other religions besides Judaeo-Christianity; they're like the colour-blind people. But to the atheists and agnostics who may somehow stumble across this blog (yeah, right, but God does work in mysterious ways), think very long and very hard about your own preconceived ideas and skepticism. Aren't you acting a great deal like a blind man, who never having either the equipment or the experience, cannot conceive of such a thing as vision and does not believe in it? Indeed, the blind man has it far more right when he says, "Sight may be true and right for you, but not for me".
All throughout my life as a Christian, I guess I have always been wondering how best to share the Gospel. Only last week did I come across this tactic - throw the question back at them. How would you explain something so fundamental to your life to someone who has no personal or rational reason whatsoever to believe you? Aren't congenitally blind men believing us about sight pretty much on faith? Aren't we in effect saying "Take my word - and the word about ~99.8% of the world who can see or once could see"?
The good news is, once we were all blind like that. But Jesus came into the world to make the blind see, and so He does - both the physically blind, and the spiritually blind.
* One of them would be Clemens XII.
** You can read the full list of responses here. There are some truly strange answers, like asking them if they dream. Uh, would they dream in vision? Why would they?