Influential church historian Diarmaid MacCulloch said he believes Christianity faces a bright future, but predicted the Roman Catholic Church will undergo a major schism over its moral and social teaching.

“Christianity, the world’s largest religion, is rapidly expanding — by all indications, its future is very bright,” said MacCulloch, 60, professor of church history at Oxford University and an Anglican deacon. His latest book, “Silence in Christian History,” will be published in the fall by Penguin....