Friction makes the mind sharper. The youthful Chesterton became a Christian after reading all the avant-garde heretics of his day and concluding, "These guys are idiots" (loose paraphrase--GKC didn't use such disrespectful words).
The problem with reading heretics, though, is the temptation to see things their way. I don't know what to say about that, except that perhaps you're better off not reading them. But even if you want to take the risk, the next question is, "What to read?" Ideally, you'd find an honest atheist who asks honest questions or makes honest assertions . . . in a manageable number of pages. Few people want to read an entire book devoted to anti-Christian ramblings.
Anyway, all of this is an intro of sorts to this 1959 essay by Walter Kaufmann that I recently found online, "The Faith of a Heretic." I'm a little bit acquainted with Kaufmann's work, and he strikes me as an honest man. It also appears that Denis Dutton--a humanistic atheist--likes him. Dutton runs the Arts & Letters Daily page, and I think he's an honest thinker.
Anyway, if you want to sharpen your mind without spending too much time, you may want to check out the Kaufmann article. It might test your faith a little, but I think it'll test your mind more and make you into a better Christian thinker.
Disclosure: I haven't read the essay closely yet, much less sat down and grappled with Wally. I've skimmed through it, though, and it looks like the perfect piece to generate friction.
