David Sedaris, bestselling author of “The Santa Land Diaries,” and his sister Amy, comic actress of Comedy Central’s “Strangers with Candy,” were deemed by The New York Times as “two of the freshest satirists working today.”

Since its inception in 2001, the Sedarises’ “The Book of Liz” has been performed all over the country, skewering a wide assortment of clannish, sacred-cow communities with wacky inanity — from the Amish to 12-step recovery programs.

Why, then, is the current performance — at the nicely renovated Theatre at St. Claude and directed by Jim Fitzmorris, a welcome driving force in the New Orleans theater community — not all that funny?

The play itself, which aspires to achieve the mind-spinning hilarity and acidic wit of Christopher Durang or Charles Busch, is at best a slight, off-kilter bit of mockery that would take the most expert of comic actors to pull off.

The story revolves around Sister Elizabeth Donderstock (Margeaux Fanning) who lives in Cluster Haven, home of a conservative Christian community called the Squeamish. Here, she makes the vastly popular cheeseballs which provide her clan its largest source of income.

But Liz is unfulfilled, and her desire to lead the chastity parade is thwarted by the overbearing, dour Reverend Tollhouse (Kyle Daigrepont).

“Do you ever get the feeling that you’re not being appreciated?” confesses Liz to her cult comrade Sister Constance Butterworth (Kathryn Talbot).

When her culinary duties are replaced by Brother Brightbee (Joel Derby), Liz runs away and has a series of preposterous adventures before ultimately returning to Cluster Haven a supposedly changed woman, content and respected by the members of her commune.

Primarily staging his actors downstage and resisting all forms of physical comedy — except the amusing use of a spray bottle to keep Liz sweating — Fitzmorris directs the action like stand-up comedy, placing the burden on the comic technique of his amiable cast.

The four-member cast manages the multiple roles favorably, creating 15 eccentrically engaging caricatures, each based on one or two dominant traits.

Daigrepont is at his best as Duncan Trask, the effete 12-stepping manager of a pilgrim-themed diner. Derby alternates well between the bright-eyed Brother Nathaniel and the roughneck Danny Polk.

Talbot takes on the biggest challenge, producing six unique personalities ranging from busybody Sister Elizabeth to the Cockney-spouting Ukrainian Peanut to AA life-sharing Dr. Barb Ginley.

Fanning, the most natural actor of the group, holds the lead fittingly, but could stand to let the zaniness affect her in more wild and extreme ways. At present, she seems trapped in a small assortment of responses.

As directed by Fitzmorris, the cast thankfully resists cartoonish silliness or, worse, in-on-the-joke self-parody, but unfortunately they fall short on the necessary comic inventiveness and dynamics to maximize the effectiveness of this 85-minute skit.

Part of the problem may lie with us and our level of expectation for such Saturday Night Live-style wackiness. From Gilda Radner and Tracy Ullman to Jim Carrey and David Chappelle, due to television, the bar has been set high.

The role of Liz was written to showcase the comedic gifts of Amy Sedaris, who spent five years with Chicago’s Second City comedy club honing her chops. This is tough competition.

Sketch comedy hinges on the manic spirit of improvisation, spontaneity unleashed — that in-the-moment thrill of “We’re making this up as we go along.” Fitzmorris’s diligent cast hits things a bit too hard for the hilarity to truly soar.