A bronze statuette stands on top of a cabinet, depicting a figure in a wide-collared shirt unbuttoned to the chest, a big blow-dried sweep of hair with emphatic sideburns, beautifully angled eyebrows, and a rictus grin. This is a typical image of Neil Diamond — macho, cheesy, a guitar man in a florid shirt.

“The shirts have been a big distraction,” Mr. Diamond said. “Imagine my career without the shirts.” As if to make a point, he is wearing a faded black T-shirt, with a black baseball cap pulled over unruly hair. Sitting with a decaf cappuccino in a room crammed with posters, platinum discs, and cardboard cutouts depicting a swaggering figure in a succession of extravagant shirts, the man himself seems barely recognizable. At 67, he resembles a fit but dowdy pensioner. The handsome features are weathered by age, deep furrows in his rough skin, earlobes stretching, dark eyebrows bushy and tinted gray. But it is his sense of brooding gravity that seems most removed from the bristling energy of the figurine.

“It’s the yin and the yang,” Mr. Diamond said, in a gravelly, somber voice. “The performer is the extroverted, open person willing to make a fool of himself, who wants to laugh at himself, and to enjoy life openly and freely. I need that so that I can do the other thing. If I just did the writing, I would have been in a mental institution years ago.”

This may seem glib, but I don’t think Mr. Diamond was joking. He has a very particular way of talking, slowly and thoughtfully rubbing away at a topic in long, poetic phrases. He clearly takes his craft very seriously. “It’s grunt work, pure physical labor,” he says. “It’s ditch-digging, and unfortunately the ditch that I’m digging is inside of me.”

Mr. Diamond has sold more than 120 million records worldwide and remains an incredibly popular live attraction. He brings his band to New York’s Madison Square Garden on August 12, 14, and 15. The memorabilia of a career spanning five decades is dotted about an otherwise elegantly discreet studio complex close to Beverly Hills, Calif.

But if you examine the content of the songs on which his fame is based, the showbiz veneer peels away and another side of Mr. Diamond is exposed. This is the Solitary Man depicted on his first hit in 1966; the literate, thoughtful, and melodically adventurous composer of songs that cover a vast array of moods and emotions, from the celebratory “Sweet Caroline” and “Cracklin’ Rosie,” to the spiritual aspirations of “Holly Holy,” the everyman stoicism of “Song Sung Blue,” and the raging existential angst of “I Am I Said.” Part of the appeal of Mr. Diamond’s music is surely its range: “Just as life has very deep, dark moments, it also, hopefully, has its shiny, happy moments, and that makes for balance,” he said. But the bedrock of his writing is a probing examination of self. This is the ditch he refers to.

Mr. Diamond’s new album, “Home Before Dark” (out May 6), was written and recorded in a year. “You can put in however many hours you want, and I put in every hour that I’m awake. Whether I have a piece of paper in my hand or not, I’m writing until it’s done.”

One song, “Act Like a Man,” questions Mr. Diamond’s entire oeuvre, referring to the “songmaker” as a “heartbreaker,” “faker,” and “worthless daydreamer.”

“You get to sing and dance all day, like children playing,” he sings. “But it’s time to act like a man.”

“There’s a lot of talking to myself in the songs,” Mr. Diamond said. “That song is an exploration of how I’ve spent my life and whether I’ve been honest or just a poser. What is this thing? Does it have any value?”

Born in 1941 into a Russian-Polish family (“Diamond” is his given name) in the New York area, he moved homes frequently, attending nine schools. The family eventually settled in Brooklyn, where his father owned a dry-goods store. Mr. Diamond started guitar lessons at 16, in part to try to overcome his shyness. “I got hooked when I wrote my fifth song,” he said.

Mr. Diamond spent his early career as a staff writer in the legendary Brill Building. American-manufactured Beatles clones the Monkees brought Mr. Diamond his first success with versions of “I’m a Believer,” “A Little Bit Me, A Little Bit You,” and “Look Out Here Comes Tomorrow.” He signed his own recording deal in 1966 and scored immediate pop hits, but always felt out of step. “The Beatles ruled the world, and here I was, another guy with sideburns and a guitar, Elvis 10 years later. Nobody was really paying attention, not even my manager.”

Mr. Diamond appears genuinely to feel he has always been out of favor with singer-songwriter contemporaries and critics. And he is convinced that the reason has nothing to do with music.

“It was the shirts,” he said. “For better or for worse, the shirts created an image in people’s minds of what I was. I just wanted to have some fun with it. So my clothes designer started to make these fantastic shirts, and they got more fantastic as time went on. We probably stayed with it too long, we had too much fun with it. The shirts became a rebellion for me, a way of removing myself from a group that would not accept me anyway. ‘You don’t like it? I’ll take another dozen.'”

In 2005, a stripped-back, acoustic-flavored album, “12 Songs,” recorded with producer Rick Rubin (Beastie Boys, Slayer, Red Hot Chili Peppers, Johnny Cash), forced many to reassess Mr. Diamond. It received the best reviews of his career, yet Mr. Diamond said he is unmoved by anyone else’s opinion. “What drives me is the hope that I can create something beautiful. Even if it means spilling my guts, then so be it. I have created children, I will never create anything as beautiful as them, but this is something that’s mine. And if I decide to do it, I must do it with everything I have.”

The new album is, if anything, even more stripped down, yet there is a warmth to the musicians’ interplay and a quality of emotional commitment in the songs that makes it hugely engaging. It touches on many of the themes, lyrical and musical, of Mr. Diamond’s career from the perspective of a man still wrestling with the big questions, but it is not bleak. He admits, however, that it was “a difficult album to make” during “the most difficult year of my entire life.” His somber mood is later explained when it is disclosed that one of his oldest and closest personal friends is nearing death.

“Someone that I loved very much was going through an extraordinarily difficult time,” Mr. Diamond said. “And so I had to bear that and still try and create something beautiful in a time of extreme distress. It made it a test. I am sure a lot of that came out in the songs, and so be it. I had to find something to hold on to in that storm, grasp at jagged rocks and keep from drowning, and find any consolation out there to carry me through.”