Prophesy: What is it good for?

I'm in a group studying Isaiah this year (a small group Bible study with Graduate Intervarsity). Since Isaiah is a book of prophecy, the question naturally arises: What is the purpose of prophecy? Two purposes, actually. What was the purpose for the intended audience of the time, and what is the purpose for it now, for us? (Assuming that it was kept in the canon for a reason, and therefore does have something to teach us.)

It's common (and easy) to think of prophesy as a telling the future (like a fortune teller), or a checklist of future events. I suspect this is partially due to the two major Christian events - Christmas and Easter - being associated strongly with fulfillment of various prophecies. (Side note: even in these cases, what is the significance of the prophesy being fulfilled? Is it just a checklist on some countdown to Armageddon, or something else?)

One practical problem with treating prophecy as a checklist is connecting the portended events with historical events. In the study, we were confused about the beginning of chapter 22, but turning to Oswalt's commentary we found, "The historical setting of vv. 1-14 has been the cause of a great deal of scholarly interchange." The experts and scholars don't know - how are we supposed to be able to understand it. And if understanding a precise connection of the prophecy to history is a prerequisite for understanding the prophecy, this is a problem.

Another problem with the checklist approach is that it doesn't help with the question of meaning - especially the question of what does it mean for us today.

In wrestling with some of these questions, an analogy occurred to me. Comparing prophecy to anti-drug ads or anti-smoking ads. My favorite was "This is your brain (picture of an egg). This is your brain on drugs (picture of frying pan smacking the egg)."

Imagine an anti-smoking prophet approaching a smoker on the street, saying "You're going to die. Those cigarettes will give you emphysema and lung cancer. Not to mention yellow teeth, bad smelling clothes, and a 50% increase in alien abductions"

Now, what is the point? The smoker may not suffer all, or even any, of those consequences. They may get hit by a bus instead. But suppose they do get lung cancer - what was the point of the anti-smoking prophet? To provide a checklist of future events? The smoker then can see what the prophet was predicting, but it doesn't do them much good then. In this analogy it seems the point of the prophecy is a warning of the consequences, and to give a chance to change behavior.

I can think of a couple questions from this: First, what do these historical prophecies tell us about the nature and character of God ? Second, more of an application - are there any areas in our lives where we know truth about our actions, but are ignoring the consequences?

[Edit 1/12/2005 - changed the ending somewhat]