Years ago, I heard soprano Renata Scotto give a master class to an unknown young soprano named Sondra Radvanovsky, who is now a star in her own right. One thing Scotto said has stuck with me. She was talking about conveying emotion onstage, and she pointed out that if a singer actually cries when her character is supposed to be crying, she will not be able to sing. The trick, she said — and I paraphrase — is to convey the sense of the tears while keeping your emotions removed enough that you are able to produce the notes.

That story came to mind Thursday night as I listened to, and watched, conductor Christoph Eschenbach — with the string players of the National Symphony Orchestra — fling himself into Richard Strauss’s “Metamorphosen” in the Kennedy Center’s Concert Hall. Eschenbach puts his whole heart out onstage, every time. “Metamorphosen” is an aching 26-minute work for 23 strings, written at the end of World War II and drenched with the German composer’s longing for a lost past amid the rubble of his country. It’s a story that Eschenbach, who survived a World War II displaced persons’ camp, can relate to, and he certainly felt every bit of it.

Yet his performance sounded as if, in Scotto’s example, someone were actually crying rather than conveying emotion through music. The balances were off, the textures were a little muddy: I saw the pain, but it didn’t move me.

That kind of involvement is at once the best and worst about Eschenbach’s approach. It’s the worst, because the performance could be so much better. But it’s the best, because how can you fault someone for getting so involved with a moving work of art, and for caring about his musicians so much, that he shook hands with every one of them when the piece was over?

Anyone who bemoans how big symphony orchestras can fall into routines should come watch Eschenbach. There’s no routine in his work; he’s reinventing the wheel every time. That is the reason some big orchestras have looked down on him, thinking he doesn’t know better. It’s also the reason many musicians would follow him to the ends of the earth: Because this kind of sincerity and honesty is rare.

Christoph Eschenbach, right, directs the National Symphony Orchestra at the Kennedy Center. (Bill O'Leary/For The Washington Post)

There’s no right answer, only the way each performance happens to hit you — and the unevenness is a byproduct of the excitement. To me, “Metamorphosen” failed to come across well Thursday, but Beethoven’s “Eroica” symphony had a lot of pizazz and energy, and it mostly kept me riveted. Eschenbach’s approach keeps the music fresh; it’s as if he were discovering it along with the listener — and were surprised a little, each time, at how it comes out.

In the face of so much genuine excitement and feeling, in a field that desperately needs more of both, it can seem beside the point to single out things that didn’t work — especially in a performance that offered a lot to like. Yet the idea of excellence in music is traditionally about going beyond mere feeling. Eschenbach’s expressive points were blunted when the mystery of the strings’ quiet chords in “Eroica’s” first movement was answered by winds that sounded downright pedantic. Or when, in “Metamorphosen,” the lyrical solo line of the concertmaster, Nurit Bar-Josef, was submerged in a fuzzy sea of dark sound from the other surging strings.

There’s an obvious connection between the two works: The theme from “Eroica’s” second-movement funeral march permeates “Metamorphosen,” emerging time and again in a gesture of sorrow like the beating of a breast. That referentiality made for an inward-turning program on an inward-turned night that featured Eschenbach and his orchestra, without the intermediary of a soloist.

And if to my ear it offered too much of the musical equivalent of Method acting, it had virtues that too many orchestra concerts lack these days and appeared to delight the audience, which greeted it with warm applause.