I preached on David and Goliath yesterday. My sermon is just a series of notes so it won't be reprinted here, even in abridged form, but the more I read that story, the more I liked it. And here's what I liked about it: the faith that David displays is not magical thinking.
By "magical thinking," I mean when people say, "God will provide" without making any plans or taking any steps themselves. I first realized David is not this kind of person when I noticed he took 5 stones for his sling. Five. He's a confident little twerp, but he's not stupid.
I also noticed that he had some experience and evidence to back up his sense that he could take Goliath out with a sling. He explains to various scoffers that he had been able to kill lions and bears by this method, so he has some reason to believe that he can do the same with this Philistine.
Finally, I noticed that, unlike what we normally think when we say "David and Goliath," with a little guy alone against impossible odds, David actually has an army behind him. Literally. The odds were a lot better than you might think.
I know I'm speaking for myself here rather than God, but my feeling is that God doesn't want us to be courageous in a stupid way. And that's one thing that David demonstrates is smart and strategic courage. I think we'd do a lot better at standing up against injustice if we were more prepared and strategic as we did so. My two cents.