Yeesun Kim says she and her Peregrino Zanetto cello, built in 1576, have a happy marriage. She accepts its shortcomings — its struggle, once, to project powerfully enough against an orchestra during a performance of Shostakovich’s first cello concerto — and appreciates its fine qualities, including a delicate, mellow sound well suited to blending in chamber music.

In rehearsals and performances with the Borromeo String Quartet, of which Kim is a founding member, the cello is both agile and weighty and speaks in rich tones that both shimmer and sing. The other members of the quartet are violinist Nicholas Kitchen, who is married to Kim, violinist Kristopher Tong, and violist Melissa Reardon. The quartet will perform in Wellfleet at the First Congregational Church on Friday, Aug. 2 at 5:30 p.m.

The two pieces on the program are Beethoven’s String Quartet No. 16 in F Major, and Schubert’s String Quartet No. 14 in D Minor, “Death and the Maiden.” Kim describes both as among the greatest music ever written for the string quartet.

“There’s a reason why certain classical pieces survive the test of time,” she says. “They express things that we as human beings can tap into at every stage of our lives.” There is a sense, she says, that there is a “greater truth” behind the music.

The Romantic era in music, roughly corresponding to the 19th century, was a period that embraced that feeling: at its center was the idea of “the infinite,” a realm of expression that defied the limits of verbal distinction and that instrumental music could reach for through the evocation of deep, wordless emotion.

Beethoven, in his later years, composed on the cusp of Romanticism. His String Quartet No. 16, Opus 135, was not only his last string quartet — it was his last complete composition of any kind, finished in October 1826. He died in March 1827. The piece has a more standard four-movement structure than the radically innovative quartets that preceded it — like Opus 131, with its seven movements played without a pause between them.

Opus 135 is comparatively moderate and refined and at the same time a masterful example of the composer’s confident and uncompromising style. The first movement is an Allegretto, lyrical and sweet, but excitingly contrapuntal. The second movement, Vivace, brings to mind the drunken frivolity in Beethoven’s sixth symphony, “Pastoral”: the first violin sounds more like a fiddle, playful as a kitten above the roil and toil of the others. The third movement, Lento, is as tragic as it is euphoric — as close, perhaps, as Beethoven comes to expressing a sense of the divine.

Above the final movement, the composer wrote this motto: “The difficult decision — Must it be? — It must be, it must be!” Was he confronting the knowledge of his mortality? The opening Grave speaks the question in a chilling three-note motif. The ensuing Allegro shouts the answer with two three-note motifs, and a musical journey unfolds before the piece ends with a final, triumphant cadence.

Like Beethoven, Schubert lived in the years that spanned the end of the Classical and the beginning of the Romantic eras. He composed his 14th quartet, “Death and the Maiden,” in 1824 and titled it after the theme from its second movement, Andante — the theme itself borrowed from a song he had written seven years earlier, “Der Tod und das Mädchen,” in which gentle death consoles a terrified, doomed young woman.

Schubert had contracted syphilis two years before he wrote the quartet, a diagnosis that plunged him into a deep, ultimately inescapable depression. In the years that followed, death hung heavily around his shoulders. It’s impossible to analyze “Death and the Maiden” without an awareness of the context of its composition. The first movement, Allegro, is lyrical and fast-paced, though it isn’t over quickly — it’s almost 16 minutes long. The right word for it might be “desperate.”

The second, song-like movement is similarly long at 14 minutes. The first violin sings its plea, high and clear, sometimes shrill and sometimes as delicate as lace. The conversation continues, burdened by tension. The third movement takes the form of a Scherzo, aggressive and unsettling; then relaxes into a soft candy center of a trio, gentle and in the major key; then back to the scherzo, never happy for too long. The final movement, Presto-Prestissimo, is a manic, morbid dance.

Both pieces are celebrated; both have been performed countless times by countless quartets. To approach the music with a fresh perspective, Kim says, the player cannot be self-conscious. “The music itself has its own demands. We’re recreating it every time. It evolves on its own.”

When programming repertoire for a season of performance, the Borromeos will pick a certain number of older pieces that they want to play again. “Just by the sheer force of practicing and thinking about that music,” she says, “a new level of insight settles in.”

Rehearsals are less about the physical act of playing, says Kim, and more about learning how the four players hear the contours of the phrases, the relationships between movements, and the greater architecture of the piece they’re working on, and then enacting their unified vision.

The performance, she says, is the moment that tells the quartet whether rehearsals have been successful. Under pressure, in concert, the Borromeos are in their “fully concentrated form” and “carry the responsibility of speaking through the music.” This process is true for any composition, says Kim.

She recalls the day, years ago, when her young child broke his leg. That night, the Borromeos were to perform the full cycle of Bartok’s six quartets. She turned up to the venue five minutes before the concert. During the three hours of performing, she says, the chaos of the day left her mind completely. It had to. “The Bartok quartets are no small matter,” she says. “If you get off, you’re off.”

When playing such great music as the Beethoven and Schubert, says Kim, a similar transcendent concentration must occur: “The clarity of what needs to be done is alarmingly definite.”

The Borromeos also frequently perform new compositions by contemporary composers, though none are on the program here this summer. In performing new pieces and the masterpieces of old, Kim thinks of the work in absolutes: “Music has to be played. It cannot just sit in the drawer. It’s our duty to play as much music as possible and to share it with the general public.”

It is impossible to truly know the motivations of long-dead composers, but for Kim, in the cases of composers both living and dead, speculation is interesting enough. “Trying to get to whatever it is that brings people to create something and being a part of the creative process,” she says, “is endlessly fascinating.”

The Show Goes On

The event: Borromeo String Quartet performs Beethoven and Schubert
The time: Friday, Aug. 2, 5:30 p.m.
The place: First Congregational Church, 200 Main St., Wellfleet
The cost: adults $40; students with ID $20; children under 14 free