Heather St.Clair’s phone peeks out of the plum, pleather laptop bag she totes around a women’s retreat in Lynchburg, Virginia. Before dinner with friends, she grabs the phone, swipes the oversized screen, then flashes a smile. “I just made $50!” she announces.

Last year, St.Clair became a seller with Thirty-One Gifts, a Christian-owned company that makes customizable bags and accessories. She wanted to get a deal on her laptop bag, and has since hosted 22 parties—in person, through catalog orders, and online. In July, the 38-year-old mother of four drove six hours to attend Thirty-One’s national conference in Columbus, Ohio.

There, the arena glowed pink from the crowd of 9,000 women dressed to match the signature magenta logo. Each wore a string of ribbons designating their achievements and goals: “Paid off debt!” “Empower women!” “Live for me!” Thirty-One Gifts has drawn in 300,000 sellers since Cindy Monroe founded it in 2003.

“We are a business that’s helping women make more income so they can reach their dreams and look for what God’s calling them to do,” said Monroe, 41, who named the company for Proverbs 31’s Wife of Noble Character.

Last year, Thirty-One Gifts brought in $643 million in revenue—more than popular purse line Vera Bradley, whose annual revenues average a half-billion dollars. Monroe recently appeared on a Forbes “Businesswomen to Watch” list. Her estimated net worth matches that of pop star Taylor Swift. “I want women to have the courage to think outside their box,” Monroe said.

As American women think outside the traditional boxes of “work” and “home,” ...

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