The American archbishop who welcomed Pope Francis to the final rally of his U.S. tour has warned that Francis' big family summit of bishops risks doing serious harm to the Catholic faith if it endorses changes to the church's practice on marriage.

Archbishop Charles Chaput of Philadelphia took to The Wall Street Journal on Friday to explain the "anxiety" felt by many bishops that a change in the church's practices of ministering to divorced and civilly remarried couples could eventually lead to a change to its doctrine on marriage.

He warned: "Practice inevitably shapes belief."

Countering his alarm was another American. Archbishop Blase Cupich of Chicago, hand-picked by Francis to join the synod on the family, told reporters Friday that "I don't share the anxiety."