In a letter from Rome in April of 1770, Leopold Mozart, father of the composer, reported to his wife on his son’s latest musical triumph. “You have no doubt often heard of the famous Miserere, which is so highly treasured that the musicians of the Chapel are forbidden, under pain of excommunication, to take a single part out of the Chapel, to copy it, or to give it to anyone,” he wrote. “We now have it: Wolfgang wrote it down.”

The note illuminates two attributes that characterized the genius throughout his life: Even at the tender age of 14, there were, for Wolfgang Amadeus Mozart, no musical secrets. And he had little tolerance for frivolous dictates, no matter how powerful the source. This latter, of course, would have consequences: Indeed, his sister-in-law Sophie reported that, as Mozart lay on his deathbed, she attempted to fetch a priest, but none would come. But the composition Mozart was hurrying to finish during his final illness was a Requiem mass. (The work had to be completed by his student and copyist, Franz Xaver Sussmayr.)

That powerful and influential Requiem will be performed Friday and Saturday evening to conclude the season’s Mostly Mozart Festival at Lincoln Center: a fitting climax. Friday’s program also features, however, what must be the oddest pairing at this or any other Mostly Mozart concert in memory: As a prelude to the Requiem, audience members will hear extended Persian and Indian improvisations performed by the group Ghazal. On the surface, the contrast couldn’t be greater.

Mozart was capable of natural simplicity and balance; his music, wrote Eugene Delacroix, “suggests the calm of an orderly epoch.” Indeed, the motet Ave verum corpus, also written in the last year of his life, is the very embodiment of grace. But his Requiem is scored for large forces. It is a great, passionate, dark, and unsettling work – Beethoven found it “too wild and terrible”- that pushed the limits of the classical tradition in his day.

The commission for it came anonymously, through a messenger sent by Count Franz von Walsegg, who intended to have it performed at a memorial service for his late wife. The reason for the secrecy is clear: The count wanted to pass the work off as his own. Evidence suggests Mozart knew the real facts, but needed the money. Nevertheless, from the very first biography of the composer, a legend grew: Mozart was pursued by the messenger, who “appeared like a ghost,” demanding to know when the Requiem would be delivered. The dying composer supposedly became obsessed with the thought that he was writing the work for himself. The confluence of events was certainly eerie: A bedside witness reported that Mozart’s very last action “was an attempt to express with his mouth the drum passages in the Requiem.”

In comparison to the Requiem’s powerful array of chorus, vocal soloists, and orchestral forces, Ghazal presents music of a far more intimate nature. On their recent CD “The Rain,” Kayhan Kalhor on the kamancheh (a bowed instrument), Shujaat Husain Khan on the sitar (as well as vocals), and Sandeep Das on tabla, engage in long, sometimes wistful and often animated interactions based on Persian and Indian melodies. The playing is beautiful and inventive and the musicians demonstrate a remarkable level of ESP while responding to each other in the moment. The result is not Indian or Persian in the traditional sense, however, but world music as filtered through a modern lens.

This shows up in the group’s extraordinary attention to instrumental color, in their very contemporary sense of dramatic shape and climax, and in the simple rhythmic schemes of their playing. Westerners can relate more easily to this music, based on groups of 3 or 4, than to the asymmetrical, long rhythmic cycles found in traditional raga. “Rhythmic cycles can be difficult,” said Mr. Kalhor. “In this and other respects, we don’t feel we have to move within the traditional boundaries or rules. We like having the room to be ourselves.

“Our understanding is based on melody,” he continued. “I was raised in a Persian musical culture where we have a huge collection of patterns to memorize – whole phrases, sometimes up to a minute of music at a time. And there are more than 400 of those in different scales. Shujaat Husain Khan was raised in an Indian culture, but we have no trouble finding a commonality. In our minds and in our hearts the music already exists, and we only have to translate it into a new language.”

One interesting aspect in the music is the degree of improvisation. “We improvise about 95% of what we play,” said Mr. Kalhor. “I have never felt as musically close with any other musician in my life.” Improvisation, he pointed out, is one possible parallel between the two musics. “Improvisation used to exist in Western classical music as well,” he said. “Composers were often virtuosos who simply notated their improvisations. To this day, a composer in my culture begins as a virtuoso on an instrument.”

Ghazal’s music is first-rate, but I still wondered at the pairing. “At first, it didn’t make sense to me, either,” said Mr. Kalhor. “But not only Mozart, but many Western composers used musical elements from the East.” There are certainly Eastern elements in Mozart’s Piano Sonata in A with its “Turkish Rondo,” and in his opera “The Abduction from the Seraglio.” Similar influences can be found in Haydn and Beethoven.

Yet, why not place Ghazal in the context of some of Mozart’s chamber music, or along with, say, the slow movement of the early Piano Concerto in E Flat, K. 271, a work steeped in spaciousness and inspired delicacy?

“The idea was to focus on some of the universal themes in Mozart’s music,” said Jane Moss, vice president of programming at Lincoln Center. “We wanted to place the Requiem, a deeply spiritual piece, with other musics of the world-to touch on other cultures with similar themes. The feeling may be expressed differently, but it moves the human spirit in the same way.

“You also hear the Requiem differently after listening to Ghazal,” she explained. “This was an idea of Music Director Louis Langree. We listened together to about 40 CDs of music from around the world. But within 20 seconds of listening to “The Rain,” we knew this is what we should do.”

Ultimately, the juxtaposition of these two musics is simply part of an ongoing dialogue that Mozart himself took part in. “The exchange of musical ideas has been going on forever,” Mr. Kalhor said.

And how will the audience react? “It’s going to be interesting to see,” Ms. Moss said. “To tell you the truth, I’m most interested in what the Ghazal fans will think about the Requiem.”