Brett Dennen at ACL Fest on Sunday, Oct. 9, 2016. Erika Rich for American-Statesman

“It’s not too hot, but the sun is out, and you look beautiful,” beamed Brett Dennen as he and his three-piece backing crew locked into a perfect just-past-noon vibe on the Samsung stage for the final day of the Austin City Limits Music Festival.

“I appreciate you coming early to hear us,” he added,” and the modest-sized crowd clearly was equally appreciative. Dennen’s music — a mix of bright acoustic pop, laid-back electric reggae and smooth-sailing island groove — proved an ideal day-starter on the fest’s largest stage, a prelude to great things to come later from the likes of Willie Nelson, Nathaniel Rateliff and fest-closer Mumford & Sons.

Up front, devoted fans sang along to hits such as “Wild Child” (perhaps an inspiration to the Austin band of that name?) and “Cassidy.” On the fringes, both couples and singles found their own individual ways to be moved by Dennen’s highly danceable tunes.

As instantly likable as Dennen’s sound is, the lyrics sometimes are deceptively intriguing and challenging. On “Make You Crazy,” he sings of “cameras in the sky” and “lasers in our living rooms” even as the music draws you in with a mesmerizing melody. And his conclusion, after listing a litany of worries in the modern world, is insiprational: “Don’t hesitate to speak your mind, never hesitate to speak your heart.”

He practiced what he preached toward the end of the set, with extended and humorous introductions to the terrific one-two finale of “Wild Child” and “Sydney (I’ll Come Running).” Before giving his bandmates due credit — drummer John Radford, bassist Daniel Rhine and guitarist Rich Hinman — he ruminated at length:

“Take care of yourselves, OK? Be nice to each other. And if you have fair skin, cover up a little more. … And remember, just because beer has water in it, doesn’t mean you’re drinking a glass of water! … I know that there’s a debate on tonight, but you know what the outcome’s going to be. Just focus on making this place a better world.”

That’s Brett Dennen, never hesitating to speak his mind and his heart.

(Pro tip: If you’re on the ACL Fest grounds this afternoon, Dennen is playing the final informal acoustic set on the Lowe’s Studio stage at 3 p.m.)