ORLANDO, Fla. — In the pews of the First Baptist Church of Orlando, where thousands of evangelical Christians gather on Sundays to worship and sing, a change of heart is happening on the once toxic issue of immigration. Two years ago, national evangelical leaders began to speak out in favor of legislation to give legal status to immigrants in the United States illegally. Now, as Congress is about to start a debate on overhauling the immigration system, conservative Christians in those churches, once inclined to take a hard line on immigrants they viewed as lawbreakers, are consulting their Bibles and...