HUDSON, N.Y. -- What's in a beard?

For Hassidic Jews whose observance calls for a uniform outward appearance, including hat and long beard for men, the bushy, black beard of unlikely reggae hero Matisyahu was a manifestation of his devotion to the faith.

So when he tweeted a photo of himself a year ago, clean-shaven, with the self-aware caption "No more Chassidic reggae superstar," it was the Dylan-going-electric of ultra-observant Jewry crossing over into popular music.

Since then he's released a new album -- his most mainstream yet -- reflecting the ongoing spiritual journey that remains at the heart of his music and, as he tells it, his life.

"There's a lot of talk about sparks and mystical ideas about the creation of the world," he says of his new album title ("Spark Seeker") and its relation to the branch of Jewish mysticism known as Kabbalah, "but the basic gist of it is seeking a spark in your life, looking for meaning, looking for that light, that thing that makes life comes alive. That's what it's always been about for me since I was a young teenager. It was, searching for that spark within, inside and outside, in the music -- searching for it."

He plays an intimate acoustic show at Club Helsinki Hudson on Monday.

Matisyahu emerged with his debut album in 2004. On first glance, the juxtaposition of Jamaican-born musical flavor with this artist's heavily Jewish themes and wardrobe of black suit and wide-brimmed hat -- as favored by the Brooklyn Hassidic community he adopted in his late teens -- might have seemed a novelty.

But the roots-inflected sound and his nimble verbal firepower were simply too righteous to dismiss. "King Without A Crown," in which he sings praises for God and calls for the emergence of mashiac, the Jewish messiah, was a Top Forty hit and a certified gold record.

Some more contemporary, and even commercial, sounds have entered his recent work; the latest effort was produced by Kool Kojak, best known for work with big-selling artists like Ke$ha and Nicki Minaj.

"I love the reggae, I love hearing Bob Marley and all those different artists and the way they were incorporating Old Testament, and I felt my identity as a Jew with the music. And when I started singing, that's the style I was singing in," he says of his ongoing musical development. "Kojak brought out the style of music that he makes, connected with one side of my musical creativity, one aspect of the type of music I wanted to make."

He describes an artistic evolution with no space for looking back -- he seldom listens to his old stuff once he's toured behind it, he says.

"When I listen back to a lot of that stuff, I appreciate it, the words and what it did for me at one point. But I feel I've come a long way. It's almost a little painful to listen. I feel I'm getting better, basically. Even though those songs were great, I feel more solid."

The radio-rap flavor on "Spark Seeker" could be the beginning of a new direction, or maybe just a sideways step that the next album will pass by. Indeed, his just-released holiday single, "Happy Hanukkah," strikes more of a balance with the earthy, old school reggae of his earlier work.

His acoustic show highlights a different element of his sound than the hard-driving, rock-inflected concert persona he's featured on two live albums. In this setting, for instance, he's more likely to launch into a cappella beat boxing, in the hip hop tradition

"The show with my band is pretty much a rock show, is the best way I can describe it. It's different styles of music but everyone is up and dancing. It's a sweaty kind of thing," he explains. "This is sit-down. You can really hear the voice and the subtleties in the music. It's a completely different kind of dynamic."

There's a shape-shifting element to some of Matisyahu's story, but it's also a tale of self-invention. There's opportunity to be cynical about the whole enterprise, but that only gets easier if you stick your fingers in your ears. 

It's all a reflection of that spiritual journey, he says -- one that leads to twists and turns in his outward observance of Judaism, or of the production elements of his records, but in a sense remains constant.

"If you sat through the acoustic show, then the dub trio, then you came and saw me in South Beach, Miami with a DJ you're going to hear three completely different styles of music but it's all me. To me at least, I never feel like I'm contriving it or reaching for something outside of myself. I always feel that I'm taking and incorporating and doing different things that I know how to do, and using different colors."

What: An Acoustic Evening With Matisyahu

When: 8 p.m., Monday

Where: Club Helsinki Hudson, 405 Columbia St., Hudson, N.Y.

Tickets: $38

How: (518) 828-4800; www.helsinkihudson.com