CORAL GABLES, Fla. — He arrived a few minutes early — no entourage, just his wife and daughter — and, sweating through a polo shirt in the hot morning sun, settled quietly into the 14th row at the Church of the Little Flower.

A bit of a murmur, and the occasional “Morning, Governor,” passed through the Spanish Renaissance-style church, with its manicured grounds and towering palms, as worshipers recognized their most famous neighbor, Jeb Bush. He held hands with the other worshipers during the Lord’s Prayer, sang along to “I Am the Bread of Life” and knelt after receiving communion.

“It gives me a serenity, and allows me to think clearer,” Mr. Bush said as he exited the tile-roof church here on a recent Sunday, exchanging greetings and, with the ease of a longtime politician, acquiescing to the occasional photo. “It’s made me a better person.”

Twenty years after Mr. Bush converted to Catholicism, the religion of his wife, following a difficult and unsuccessful political campaign that had put a strain on his marriage, his faith has become a central element of the way he shapes his life and frames his views on public policy. And now, as he explores a bid for the presidency, his religion has become a focal point of early appeals to evangelical activists, who are particularly important in a Republican primary that is often dominated by religious voters.