Midway through the first act of “Broadway Songbook,” host James Rocco related what was intended to be a funny story about composer and lyricist Stephen Sondheim.

Rocco came to the punch line, and the Ordway Center audience whispered its laughter.

“Are you there?” Rocco asked.

That’s always a reliable comeback, and Rocco got the chuckles he was looking for. But the moment said something about this lethargic evening of two dozen songs by Sondheim, performed by seven singers and intercut with Rocco’s history by anecdote. The show takes a generous amount of time to rev up its energy — and even then it leaves us wondering about its sense of purpose.

“Broadway Songbook” is an ongoing series conceived as a paean to musical theater. Earlier this season, Oscar Hammerstein was featured. Rocco, the Ordway’s producing artistic director, curates the songs and writes a script that combines some basic history and a few insider tales — such as Sondheim’s complicated relationship with Richard Rodgers. Raymond Berg, ever reliable, provides the accompaniment from his piano.

Rocco has chosen an interesting mix. There are the familiar numbers, such as “Tonight” from “West Side Story” and “The Ballad of Sweeney Todd.” Others are less known and provide insight into Sondheim’s process. Jen Baldwin Peden has fun with “Can That Boy Fox Trot,” which was cut from “Follies” and later ended up in the off-Broadway “Marry Me a Little.” Kersten Rodau is terrific as she nails the Sondhiem parody, “Another 100 Lyrics.” These two performers sing words, not just notes, and that precision does Sondheim justice.

There were flubs opening night and some dropped lyrics that betrayed the show’s short rehearsal period.

There are also some odd choices. Regina Marie Williams’ silky vocal style doesn’t fit Mama Rose from “Gypsy.” That error is recompensed later, when Williams settles in nicely with “Send in the Clowns.”

Stage movement — well, to call it stage movement is generous — is left to chance, and Rocco would do well to get a better grasp on performing his written material. He reads from notes — no crime there — but some stories meander like chatter at a cocktail party. Rocco has said “Broadway Songbook” is intended as a casual affair, like friends hanging out around the piano. OK, then I want a free drink and a canape. In the end, it doesn’t matter what you call it, or what it was intended to do. Any show that requires you to get out of your house, drive to the theater, park and find your seat, should have something compelling about it.