To kick off this week’s focus on American music, Sunday’s Sacred Song Service will be led by Alice Parker, who Jared Jacobsen calls “America’s song leader.”

At 8 p.m. August 21 in the Amphitheater, Parker will conduct this week’s Sacred Song Service. She will also be involved in other activities throughout the weekend.

Parker turned 90 this year, and when Jacobsen first asked her to lead the weekend she wasn’t sure if she still had it in her. At first Parker told Jacobsen to cut back her involvement, but quickly decided to do it all.

“She said, ‘Who am I kidding? It’s Chautauqua. I’ll do whatever you want,’ ” said Jacobsen, organist and coordinator of worship and sacred music.

Parker is an American composer and arranger of Robert Shaw’s choral music. Her and Shaw’s work greatly influenced American choral music of the 20th century. In 2014, Parker received the Raymond W. Brock Memorial Commission by the American Choral Directors Association.

Suzanne Shull, project manager of the Robert Shaw website, said Chautauqua Institution wanted Parker because she’s an icon in the choral music world. As a classically trained composer and conductor, Parker has a wide perspective on music and hymnology. She will bring that big-picture knowledge of music literature to Chautauqua this weekend.

“[Parker] can get a group of people to sing who think they can’t sing, because she just sells a song to you,” Shull said. “She has a way of looking at songs that’s just completely different than most people; it’s really inspiring to hear her talking about tunes and songs.”

Parker’s weekend in Chautauqua will include several activities and events besides the Sacred Song Service. On Saturday she will teach two Special Studies master classes in composition and arrangement, and that evening lead any Chautauquans who enjoy singing through a Sing-In of some of her and Shaw’s anthems.

Shaw, who died in 1999, would have turned 100 this year. The Chautauqua Cinema will have two pre-release screenings of a documentary on his life: “Man of Many Voices.” There will be a Q-and-A following both showings with Parker and the film’s executive producer Kiki Wilson.

Parker will collaborate with the Chautauqua Choir to prepare music for Sunday’s morning worship service, and of course, the Sacred Song Service.

“[Parker] gets a group of people in a room up and singing better than anybody I know, and she does it no matter the size of the group,” Jacobsen said. “So she will get the congregation singing on Sunday morning and she will get them singing on Sunday night.”

In the Sacred Song Service, Parker will lead Chautauquans through some of her favorite 19th-century hymns and some she composed herself. Parker said she has a deep love for the form behind music and works to discover what about a tune makes it last in popularity.

“As a composer, I could say that when I was young I wanted to write big pieces, I think in the way that young people set their sights very high,” Parker said. “Now in my old age I am absolutely fascinated by what can be on one page of a hymnal. … What can be in one line of music? What is there that makes us remember it?”

Parker’s musical arrangements stretch across diverse genres and religious denominational lines.

“I just totally believe in the power of music to bring people together, to overcome the differences between people and to unite a group in a way that nothing else does,” Parker said. “And I know that Chautauqua has a marvelous history along with encouraging singing, and particularly with those wonderful hymns that have been sung in the Amphitheater for all those years, and so it’s a great privilege for me to take part in that history.”

Chautauqua community members feel just as privileged to welcome Parker. Jacobsen said the Institution always strives to feature the nation’s best musicians, and Parker is the perfect person to include.

“I hope she lives to be 150, but realistically she probably won’t, so I don’t know when we’ll be able to get her back again — but I do know that 20 years ago when she was here, she changed my life when I was just beginning my official career here in church music,” Jacobsen said. “And this year, I know that she will do things this weekend that will change my life as well.”