The conductor does double duty at this year’s Seattle Symphony ‘Messiah’

Every year, the miracle happens again: a production of Handel’s “Messiah” that is completely different from any of the previous ones. How is this possible?

It’s partly because there are so many variables in the complex score and in its interpretation. An operatic approach, an 18th-century period reading, a 21st-century modern-orchestra version — which will it be?

And then there are the questions of scale: a tiny orchestra with only one or two players on a part, or a hefty one with lots of strings and winds? The size of the chorus and the instructions given that chorus about articulation and singing style, bring in another round of complexities.

Finally, there are the soloists to consider. Has the conductor signed well-schooled oratorio singers, or opera specialists, or a little of each? And the conductor himself (or herself, though it’s almost always the former), of course, makes a huge difference in whether the oratorio seethes with drama or snores with propriety.

The current version of the Handelian classic, unveiled Friday evening in the first of four Seattle Symphony performances, is unique in this writer’s long memory of Seattle “Messiahs.”

An English early-music specialist, Paul Agnew, is not only the conductor, but also the tenor soloist. Agnew has evidently instructed the strings to play without vibrato, and most of them complied, though as Friday evening wore on, there was a fair amount of reversion to the norm.

That was not necessarily a bad thing. Vibratoless, straight-tone playing on modern instruments by musicians schooled in modern styles does not always present a happy outcome; the sound can seem scrawny and characterless.

Having your conductor also sing may sound like a great idea. In practical reality, however, this didn’t work well.

When Agnew turned his back on the orchestra (always a dangerous thing to do!) and sang his pleasantly expressive and stylish solos facing the audience, he seemed distracted — relying heavily on the score for lines that the average soloist would have managed with only a glance or two at the pages. There also were a couple of unfortunate slips that probably wouldn’t have happened if Agnew had been able to concentrate solely on his tenorial responsibilities.

When he was singing, the orchestra (under the discreet guidance of concertmaster Emma McGrath) went forward on its own. The orchestra musicians probably could have played this score in their sleep, but the conductor is there for a reason: to shape the performance and to give it meaning, unity and subtlety.

The other soloists were also accomplished and expressive: the agile countertenor Benno Schachtner, the resonant baritone Matthew Burns, and Anna Devin, a crystalline soprano who favored us with not one, but two optional and lovely high B-flats. The chorus, buoyant and supercharged, gave the performance depth and character, thanks to excellent preparation by Joseph Crnko.

The roster of principal players also included Elisa Barston, Susan Gulkis Assadi, Efe Baltacigil, Joseph Kaufman, Seth Krimsky, Ben Hausmann, Joseph Adam, Matt Drumm and trumpeter Alexander White, who gave a stylish account of the solos in “The trumpet will sound.”