keller on proverbs, via the city

In a piece on why he puts an emphasis on Christians and churches aiming to reach cities with the gospel, Tim Keller says something about the book of Proverbs that I've found, over the years, really helpful in handling the book - but he probably says it far better than I could (and the thought wasn't original to me anyway):

When I studied the book of Proverbs, I came to see that a proverb is not the same as a command or a promise. Proverbs say things like, "In general, if you work hard, you won't find yourself lacking the basics, but there are plenty of exceptions. So work hard, but don't be shocked if something goes wrong." That's not an iron-clad promise (that everyone who works hard will be well off) nor a command. It is a statement about a wise course of action. When I say that we need to put more emphasis on city ministry, I'm speaking 'proverbially.' The Bible and history shows us how important cities are as centers for ministry, yet the amount of effort the church puts into cities is not proportionate to the need or opportunity.