In this world, there are a lot of religious communities with cultural and religious diversity, including Islam and Catholic Christianity. Islam stands out with the Mosque as a Barometer and a symbol for Muslims, and Christianity with the Church as a symbol and place of religion. The phenomenon of mosques that occur today, its function and role are no longer directed in accordance with expectations. The mosque remains a place of worship, meaning it serves as a center for spiritual mental development, but the worship is getting narrower. The function of the mosque began to narrow, even though the mosque has a strategic role as a coaching center in an effort to protect, empower, and unite the ummah to realize a quality, moderate and Tolerant society. Just like mosques, today's churches that are considered ancient and outdated began to be abandoned. Jay Struck called this generation a tribe in itself." Such rapid cultural and lifestyle changes in society indirectly demand that the church make significant changes. The church that is unable to attend in its time will be destroyed and slowly abandoned by its congregation. In this thesis, the author wants to examine the actual role and function of mosques and churches, by examining how the roles and functions of the two places of worship at the beginning of the development of Islam and Catholicism as barometers of mosques and churches should be. It plays an important role for its people. At the same time comparing the role and function of mosques and churches with their communities so that it has an impact on improving the quality of faith of its adherents, because a place of worship is a means for its adherents to increase their faith by getting closer to its creator. This research is intended for: 1) To know the relationship between the existence of mosques and churches with the lives of adherents of their respective religions at the beginning of development, 2) To know the Role and Function of Mosques and Churches for adherents of their respective religions, at the beginning of development. The type of research used is a type of qualitative research. The method of analysis used is the study of comparators with the technique of literary analysis. The results of the analysis and comparison of the role and function of mosques and churches at the beginning of its development showed that the Mosque has a role and function that is more diverse from the role and function of the Church, including the Mosque is not only used as a place of worship only but as a center and center of government, Politics, economy, socio-cultural, judicial place, a place for treatment and treatment for victims of war and various things about literature and science that support the development of Islamic civilization to date. While the church only includes the role and function of administrative denomination religious traditions for Christians only.