Harbor Church sits on a street corner in Olympia, Washington, a few blocks from both the frigid waters of Puget Sound and the capital city’s vibrant, quirky downtown area. The building—modestly covered in beige siding—looks like it could house offices, but a sign above the steps to the front entrance declares its true function: “Harbor Church,” it reads, beside a logo of a tall-masted ship.

Inside, Preaching and Vision Pastor Seth Winterhalter delivers the week’s message. He’s in his thirties, wearing jeans, a button-up, and a cardigan; his head is shaved, and his beard reaches to his chest. He interacts with his congregation: inviting participation, asking questions like, “Anyone conquer death yet?” or “Anyone here feel secure?” The crowd laughs, some raising their hands. Sometimes they shout back replies. It’s a comfortable space.

A first-time visitor may never guess at the chaos Harbor was experiencing just a year ...