Preaching tells people what they need to know. Preaching to the Choir tells them what they want to hear.
Preaching to the choir will have different content depending on the audience, as will preaching proper. A Unitarian who wants to reinforce her flock’s self-esteem will, for instance, praise their tolerance and intelligence; a Fundamentalist wanting to fan fervor will praise his flock’s fidelity to the Bible and strict rectitude.
Preaching to the choir is a temptation in every age, but there’s some reason to think that an increase is a marker of impending collapse.
I’m hearing a lot of preaching to the choir as I surf the web daily. I have the good fortune of not relying on preaching or punditry for my living. I’m going to continue preaching (yeah, I’m certainly fallible, and I’ll get it wrong sometimes) and start calling out people who preach to the choir.