Experts say his two-day visit to Cuba benefits the Vatican with increased opportunity to promote the faith in a country that once imprisoned priests, confiscated church property, shuttered religious schools and deprived active Catholics of education and job opportunities.

In turn, the visit benefits the Castro brothers — ailing revolutionary Fidel and his now-ruling brother Raúl — who know the Roman Catholic Church has always opposed the half-century-old U.S. trade embargo. ...