Couldn't Leonard Bernstein just write a symphony?

Subtitles, subtexts, and tangled undercurrents abound in his three works in that medium. That’s especially so with the Symphony No. 3 (“Kaddish”), which made a rare Philadelphia Orchestra appearance Thursday at the Kimmel Center — paired incongruously with Rossini’s Stabat Mater — as part of music director Yannick Nezet-Seguin’s ongoing endeavor to make the world think again about Bernstein works that have been dismissed as self-indulgent and dated.

Musically, Kaddish contains some of Bernstein’s most formidable mid-career music, an alternately dissonant and lyrical fusion, sometimes as prickly as Schornberg’s Moses und Aron but with big tunes that recall his Broadway score. Bernstein’s controversial use of serialism in this mix is a plus, giving a sense of the music going into uncharted cosmic territory. It melds together, often with astounding sleights of hand.

This 1963 work, dedicated to the memory of John F. Kennedy, uses a feverish narration to encapsulate an era when nuclear annihilation became a possibility — giving humans a god-like power. Rage and tenderness are part of Bernstein’s disillusioned protagonist, who ultimately assumes equal footing with God. The narration is like the worst poetry Walt Whitman never wrote.

Was Bernstein just yelling at his dad? Attempts to rewrite the narration and thus re-contextualize the music have been somewhat successful to my mind. But the original version played by the orchestra Thursday prevails.

Charlotte Blake Alston filled the shoes that were once inhabited by Bernstein’s accomplished actress wife Felicia Montealegre, whose Kaddish readings were so overwrought that one critic considered calling her an ambulance. Alston brought well-considered gravity to the words.

While Montealegre’s Kaddish was an individualistic journey, Alston somehow knows how to speak for all of us. She also brought much nuance to the words, revealing their aura more than their somewhat fractured sense.

Alston aside, the performance had a ways to go.

In this challenging score, the Philadelphia Orchestra lacked the necessary hair-trigger timing. Both soprano Nadine Sierra and the Philadelphia Symphonic Choir were merely dutiful, though the Philadelphia Boys Choir sang well and seemed as alert as can be. It’s hard to say why the audience was so receptive; maybe nostalgia for the Cuban missile crisis?

Curiously, the Rossini Stabat Mater, a post-retirement work finished in 1841, was performed on a completely different level. Like Kaddish, this piece has its problems: Its religious text, about the Blessed Virgin Mary suffering over the death of her son, sometime comes with music suited to a comic opera. Orchestral gestures seem to ask, “Hey! What’s going to happen next?”

Yet Nezet-Seguin achieved a remarkably consistent tone, choosing slowish tempos that gave operatic moments more seriousness. He revealed so much previously undetected activity in the orchestration that you wondered if it had been rewritten.

Soprano Sierra returned in committed, lustrous form, though mezzo-soprano Elizabeth DeShong was the most vocally rich of the four soloists. Tenor John Osborn and bass Krzysztof Baczyk were capable but less interesting. But the Philadelphia Symphonic Choir suddenly became a high-personality ensemble with a well-textured sound and such technical confidence that unaccompanied passages stayed perfectly in tune and never drifted.

Thanks to the resulting clarity, you heard many moments that Verdi stole for his later more serious Requiem.

So Rossini ultimately accounted well for his religiosity. More than Bernstein, actually.

Then again, when posed with the question of why Bernstein didn’t just write a proper symphony, his business manager Harry Kraut once told me that, in fact, he did.

He wrote the music “and added all of that other stuff for you guys [the critics].” I don’t quite buy that. However willful, Bernstein was a deeply sincere artist. But it is an interesting thought.

The program is repeated at 2 p.m. Friday, Jan. 25, at the Kimmel Center. Tickets: $44-$146. Information: 215-893-1999 or philorch.org.