The Mostly Mozart Festival presents a distinctive opportunity in its final two weeks to enjoy a focus on contemporary Finnish music and musicians. Osmo Vänskä returns to conduct the Mostly Mozart Festival Orchestra in programs at Avery Fisher Hall.

Conductor Susanna Mälkki makes her festival debut, leading the City of Birmingham Symphony Orchestra in two large-scale works by the festival’s composer-in-residence, Kaija Saariaho. Ms. Saariaho’s oratorio, “La Passion de Simone,”sung by soprano Dawn Upshaw and staged by Peter Sellars, is performed through Sunday at the Rose Theater, with Ms. Saariaho’s cello concerto, “Notes on Light,” presented there on Thursday with soloist Anssi Karttunen, for whom the piece was written. (The program concludes with Beethoven’s Symphony No. 3, the “Eroica.”)

On Friday at 10:30 p.m. in the Kaplan Penthouse, Mr. Karttunen and pianist Tuija Hakkila will alternate Debussy pieces, including the Cello Sonata, with Ms. Saariaho’s chamber pieces, and will be joined by percussionist David Cossin for the Finnish composer’s Serenatas.

In an interview with The New York Sun, Ms. Mälkki, who is the music director of the Ensemble Contemporain, spoke of Ms. Saariaho’s concerto “Notes on Light.” The composer and Mr. Karttunen have worked for years to explore the cello’s capacities, resulting in what Ms. Mälkki, herself a cellist, said, is not a traditional concerto, in which there would be big tuttis in dialogue with the soloist.

The orchestra is rather coloring and enriching the cello sounds, and the cello part is very important for the orchestration. Skittering organic flourishes in the opening movement recall the mystic modernist Giacinto Scelsi’s sonic experiments, then more conventional passages lead to the fourth movement, which resonates as if a great metal disc dangled in a shadowed rainbow. Ms. Mälkki said the section refers to a solar eclipse: “The whole movement is just one progression. It’s fantastically beautiful, like how everything is getting cold when the sun is being covered.”

Ms. Mälkki conducted the premier of the oratorio “La Passion de Simone”in Vienna, Austria, in 2006. She spoke of the staging, in which Ms. Upshaw interacts with the dancer Michael Schumacher. “I think it’s a fantastic idea of Peter Sellars to make this juxtaposition, the inside and the outside [worlds] in a way,” she said. Of the reader’s voice, which recites prerecorded excerpts from the writings of Simone Weil, she said that “apart from the orchestral sound, there’s always this electric sound world, and the text is read with it,.” The composer emphasizes what Ms. Mälkki termed “brightness” in the large percussion section, including faint, resonant peals emitted by crotales, the tiny cymbals that figure prominently in Ms. Saariaho’s music.

Asked about timbral likenesses between Ms. Saariaho’s orchestral writing and the tapestry-like music of American composer Morton Feldman, Ms. Mälkki said both can give the impression of something static yet moving.

Friday and Saturday, Mr. Vänskä, the music director of the Minnesota Orchestra, conducts Sibelius’s orchestral suite “Pelléas och Mélisande,” with Beethoven’s Symphony No. 2 and Mozart’s Clarinet Concerto, featuring the Finnish soloist Kari Krikku. Mr. Krikku is a graduate of Helsinki”s renowned Sibelius Academy, as is pianist Tuija Hakkila, who complements her recital with Mr. Karttunen during a noon program on Sunday at the Walter Reade Theater, which matches Mozart with music by his Finnish contemporary, Fredrik Lithander.

Mostly Mozart’s artistic director, Jane Moss, told the Sun that Ms. Saariaho’s “La Passion,” which was co-commissioned by Lincoln Center and inspired by Mozart’s Requiem, became the component around which this year’s Finnish concentration was assembled.

Finland’s prominence continues next week at Avery Fisher Hall, when Mr. Vänskä leads a program of Mozart’s Symphony No. 39, Beetho-ven’s Piano Concerto No. 3 (with soloist Mihaela Ursuleasa), and Mozart’s Serenade for Winds, in which the conductor will play clarinet.

And on Thursday, August 21, at Avery Fisher, the Emerson String Quartet plays “Terra Memor-ia,” written for them by Ms. Saariaho, with Mozart’s String Quartet in B-flat major, and Schubert’s “Trout Quintet.” During the composition of “Terra Memoria,” the quartet’s first violinist, Philip Setzer, lost his mother (she’d played violin for the Philadelphia Orchestra), and that loss is said to have influenced Ms. Saariaho as she completed the new piece.