Bob Carlton names a serious problem — though I’d argue that the problem isn’t “postmodern preaching” so much as “mediocre preaching.” Modernity itself conceived and gave birth to the meaning-impaired mode of preaching that Bob has had enough of; if someone preaches in the unconvicted manner that Bob finds appalling, it’s not Derrida’s or Foucault’s or Lyotard’s fault.
People sometimes jeer at exemplary postmodern theorists, suggesting that since they cared about prison reform or the exploitation of labor or the persistent inequities associated with religious or racial or gender difference, then somehow their commitment falsifies an alleged postmodern tenet that “everything’s OK, nothing makes a difference.” (Not accusing Bob, here, by the way.) That sort of pseudo-refutation belies a tendentious reading of postmodernism that you can’t answer because it’s already decided that its postmodern object isn’t worth studying thoughtfully.) Most of the postmodern theorists I can think of adopt passionately hortatory rhetoric when you hew close to the topics about which they care most. Those simply aren’t the topics that other people have decided in advance that they should care about, or the ways that other people have decided they should care.
A long time ago, when I taught a senior honors seminar that involved postmodern theory, one of my students interrupted me toward the end of the semester and asked, “So are you telling us that postmodernism means that you’re accountable for everything you say and do, all the time?” That seemed pretty apposite for the course, for the time — and it seems apposite for Bob’s homiletical desiderata, especially when you consider that the preacher dares to stand up in the assembly of God and angels, saints triumphant and saints militant, to speak a Word of the gospel.