2 All Slovenia has continued to celebrate the work of Cyril and Methodius, well-known peers of the apostles, and the Roman Church has honored both of them with just as much fervor. The Church honored both of them in many ways while they lived, and in death it did not want to be without the remains of one of them. The Bohemians, Moravians, and Croatians were accustomed to celebrating religious feasts annually on March 9. Since 1863 Pius IX granted them permission to hold their feasts on July 5 and to discharge due prayers in memory of Cyril and Methodius. Not long after that, when the great council was held at the Vatican, many bishops humbly requested from this Apostolic See that their cult and appointed feast be extended to the whole Church. Until now the matter has been under study. But because of the change in the status of the government in those areas over the years, it seems like an excellent opportunity to help the people of Slovenia, whose well-being and salvation greatly concern Us. Therefore, We shall not allow Our paternal love to fail. We wish to promote and increase the devotion to these most holy men who once spread the Catholic faith and recalled the Slavic people from ruin to salvation. They now serve as our heavenly advocates and will powerfully defend us. Moreover, in order to bring out more fully what kind of men We propose for the veneration and worship of the Catholic world, We wish to give a brief history of their deeds.
Source: Grande Munus (Vatican.va)