Never mind he’s only in his mid-20s. He’s already conducted 22,000 performers.

The rehearsal in June at a school in Viimsi, Estonia – a Baltic coastal town that was a Soviet submarine base – ended quite a stint for Rasmus Puur. For weeks this composer and conductor had crisscrossed his native Estonia, preparing thousands of children for Laulupidu, a big choral event that happens every few years in this tiny country on Europe’s eastern frontier.

In his Bermuda shorts and a T-shirt, Mr. Puur could be mistaken for one of the young singers. Yet he’s composed an opera and created an orchestra, and he was chosen as one of Laulupidu’s chief conductors – the youngest ever for the event. At the rehearsal, the last of 73, he speaks, quietly, about “Meie” (“We”), the song he wrote for Laulupidu’s opening.

“ ‘We,’ ” he says, “tells us we don’t want to be a forgettable page of history.” In Estonia, he explains, choral conductors and composers have shaped history. For example, they helped push back the Soviets in the late 1980s. “What about you? What will your contribution be?” Puur asks. The youngsters take in the question, silently.

A few weeks later, before an audience of 100,000 at Laulupidu on July 2, the children from Viimsi merged with a choir of 22,000 youngsters on an open stage along the Baltic Sea in Tallinn, Estonia’s capital. As the singers began to swing to the rock-sounding tunes in “We” and sway together in its a cappella parts, Puur, on the conductor’s podium, was satisfied that the message he’d worked so hard to spread had reached the youths.

“The children understood,” he said after the event. “They know they can live up to their dreams.”

Generally speaking, being part of a choir isn’t something that today’s young people brag about. But in Estonia, singing is different. And the kind of message offered by Puur has resonated with Laulupidu’s participants. He’s urged them to appreciate their national heritage – and to not be part of the “brain drain” that the country has seen among young people.

As someone in his mid-20s, Puur represents a key figure in Estonia’s next generation of leading musicians who will be responsible for continuing the nation’s singing tradition.

“To have the population of one country come together ... to celebrate its historical identity through classical and folk music, that’s quite remarkable,” says Maaja Roos of New York, a conductor of Estonian descent who, for the first time, brought 60 children from the United States (also of Estonian descent) to participate in Laulupidu. The gift Puur gave the children, she says, is “the recognition that they are part of a much greater whole, a national choral identity that they will carry with them throughout their lives.”

Since its creation in 1869, Laulupidu (which also has a dance component) has been a national force. It’s credited with helping Estonia become independent twice. First, when the region was part of the Russian Empire, it gave voice to a yearning for self-determination that culminated with independence in 1917. Then, starting in the late ’80s, hundreds of thousands of Estonians took to the streets to sing forbidden songs in defiance of the Soviet regime, a phenomenon later called the peaceful Singing Revolution. Estonia separated from the Soviet Union in 1991.

Today, Laulupidu still has the power to rally. It is to Estonians a bit what Thanksgiving is to Americans: a time to give thanks for what is held dearest. For Estonians, that is their language, their culture, their identity, which successive waves of occupiers have sought but failed to snuff out.

Volleyball vs. singing

Little predestined Puur to take a leading role in his country’s biggest, most prestigious event. In high school in his native Tallinn, volleyball had priority over singing. But in Tartu, where he studied literature, he found it unbearable to be away from the orchestra he’d created at age 15. So he went back to Tallinn, where he then studied composition at the famous Estonian Academy of Music and Theatre.

He’d just graduated in 2014 when Laulupidu – the adult version of the event – was taking place. He sang in it, just as he had as a child. But this time, he says, “I was fascinated about this big machine that gathers all Estonians together, and wanted to be part of the big process.”

The calling came while performing “My Country Is My Love,” Estonia’s unofficial anthem, with tens of thousands of other singers. As people held hands and unfurled the Estonian flag, Puur grasped the power that singing has held in his country.

Well before that 2014 performance, Estonia had become independent. But still, times were difficult. The country had undergone belt-tightening so it could join European groups, notably the eurozone – and young people were leaving in droves to look for better-paying jobs elsewhere.

“I could see the headlines: Estonians are leaving!” he remembers. “But I wanted to say that not all the young people go away.”

Puur had his chance to make a statement when entries for the theme of the next Laulupidu – the youth one this July – were being solicited. His idea? To make Laulupidu about the importance of one’s roots, of learning from older generations.

In thinking about a song he hoped would be sung at Laulupidu’s opening, he gained inspiration from Anna Haava, who wrote poems in Estonia when her fellow countrymen were yearning for their first independence. “I looked for poetry to really touch and move me, to be in the service of the idea. Then the music just flowed,” he says.

Puur’s entry won unanimously, and his ideas translated into the theme of “Here I’ll Stay.”

A tough start

In the two years of preparations leading up to Laulupidu, the first rehearsals were especially challenging, Puur says. He was shy. He felt like a fool making people sing when he was barely older than them. He thought of quitting.

But as he talked about “the culture, the spirit of Laulupidu,” he saw a spark in the children’s eyes and received words of thanks. He knew he had to go on.

Beatrice Hellrand, a Tallinn middle-schooler, finds it “amazing” that Puur wrote an opera and created an orchestra at such a young age. But what impresses her the most is his connection to the choir. “He looks at you in the eyes and smiles at you, and that makes us smile in return,” she says. “That makes the song sound better.”

Marta Lee Krall, a member of the renowned Estonian TV Girls’ Choir in Tallinn, is thinking of a career in music. Her experience with Puur has given her a burst of inspiration. Conducting Laulupidu “has been Rasmus’s dream and his dream has come true, and that’s pushing me to go catch my dream,” says the 14-year-old.

Calling new conductors

On average, each Laulupidu has debuted two conductors. But Puur saw a need for more. “Many of our conductors are getting old, and we don’t want to be in a situation where all the old ones cannot do it and the new ones do not know how to do it,” he says.

As described by Heli Jürgenson, Laulupidu’s artistic director this year, Puur frenetically wrote every conducting and composing graduate in the country. It was “a wake-up call for young musicians: Please get involved!” says Ms. Jürgenson, who is the longtime conductor of the Estonian Philharmonic Chamber Choir.

So at this Laulupidu, there were 17 debuting conductors. One is Ksenija Grabova. She says that Puur’s inclusion of so many newcomers was “bold” and “important.”

Getting 15,000 children to perform “Life Is Hope and Creation” was bigger than anything she has done – and she runs three choirs in Tallinn. The song, she says, is about “carrying on [one’s] dreams and not being scared off when not everything works.”

That is part of Puur’s message, too.

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