OAKLAND -- When the rector at St. John's Episcopal Church came to Ernest Frederic Knell in 1988 asking him to step in as interim musician, he had no idea what to expect.

"Ever since high school, wherever I was, I'd always found work as an organist in a church. I'd been a parishioner and I got married at St. John's, which was the first pivotal moment," Knell recalled in an interview from his home in the Crocker Highlands neighborhood. "I remember it was the Tuesday after Easter and I said I could help out for a month. Now, I've been there 25 years."

About to be feted in a Silver Jubilee concert that Knell will direct, featuring the Chancel Choir performing Mozart's Requiem in D Minor (K.626), the longtime minister of music is philosophical.

"I was always a church musician as an ancillary thing," he said. "And I didn't have the rigidity as to what one should do."

With a successful career as chorus master for the San Francisco Opera and the wide open musical liturgy of the Episcopal church in front of him, Knell found expressing his faith through music at St. John's to be "lovely."

"The thing I learned quickly is that one had to be flexible. Congregations have different ideas about the music they like to hear. Once I got that figured out, it was, 'Oh! This is how you do this.' It was comfortable."

It's not surprising he has stayed for a quarter of a century. But his path to the position is decorated with improbabilities.

Knell grew up attending a Methodist church and learned to play piano at the age of 9. Eventually, he studied multiple instruments, playing in bands and festivals and following the musical thread weaving through his parent's social needs and spiritual lives.

"Music held everything together," he agreed, "it was an integral, natural part of life."

And so was milking cows, feeding cattle, mending fences and mowing untailored lawns on the family farm.

"I loved to run the motorized mowers," he laughed.

In the 1950s, the dairy business suffered and Knell's father decided the community needed a music store. And irises.

"We has lots of land, so we turned it into Iris gardens," Knell remembered. "I earned quite a bit of my college tuition with that. And the music store was a success."

Eventually, he had to choose between electronics and music. A visit from the Juilliard School's Abraham Kaplan, then the head of choral music at the renowned New York City arts institution, lit a spark in Knell.

From there, it was a lifetime of studying, performing, conducting and even marrying music. His wife is the gifted professional singer, Jullianne Booth. Together, they have two adult daughters and two much-loved Welsh springer spaniels.

In 2011, Knell retired from the Opera.

"It's such a lovely thing, to be home at night, isn't it?" he asked. "We plan to travel. I even love road trips to Wyoming, which is a long haul."

Finding pleasure in new places and in listening to jazz, which he said he can just enjoy, without analysis, Knell is no less excited about the upcoming concert.

"I chose the Mozart because I felt we'd gotten to the point where we could do it," he explained. "Also, Mozart never completed the Requiem and I'm using re-scorings by Franz Beyer, who believed, as I do, that other versions were not authentic."

The choir will sing the German Latin, not the Italian version often performed. The contradictory pronunciations and keeping the clarity and transparency of the rapid, 16th-note fugue sections has been most challenging.

"The key is to sort out what is what and not go overboard," Knell said.

Illuminating a text, even when it is theology that is far from contemporary, Knell insisted is "vivid and rewarding." And working with dedicated amateur singers and instrumentalists is "incredible and supportive."

Searching for what has changed over the tenure of his 25 years, he can only think of the addition of a third service to Sunday morning's schedule. Rejoicing in what has stayed the same, he said, "The marvelous, singing congregation. They really can sing and that energizes everybody."