During the second half of the 17th century, there were trends toward the secularization of the religious oratorio. Evidence of this lies in its regular performance outside church halls in courts and public theaters. Whether religious or secular, the theme of an oratorio is meant to be weighty. It could include such topics as Creation, the life of Jesus, or the career of a classical hero or Biblical prophet. Other changes eventually took place as well, possibly because most composers of oratorios were also popular composers of operas. They began to publish the librettos of their oratorios as they did for their operas. Strong emphasis was soon placed on arias while the use of the choir diminished. Female singers became regularly employed, and replaced the male narrator with the use of recitatives.