Preaching on a psalm is like trying to give a talk on "America the Beautiful" or "Somewhere Over the Rainbow." Psalms are meant to be sung—or at least read—again and again, till we know the next line before we read it, till we know their spiritual pitch without a piano introduction, till our hearts naturally begin to think and speak in psalmic.

So what's a preacher to do when our text is a psalm? We tend toward spiritual musicology, lecturing on the song's history and structure ("Do you see the chiasm in verses 5 and 6?"). We take the word pictures and deconstruct them, as if to help people find the faint blue numbers under the psalmist's paint. We rightly point out the expressions of faith or joy or pain and try to walk our people into the music, but we end up sounding like a documentary on how the orchestra works.

The preacher of the psalms is like a choral conductor rehearsing his choir. I've directed choirs for years. I'm ...