In Eastern Orthodox and Byzantine Catholic churches, an entrance is a procession during which the clergy enter into the sanctuary through the Holy Doors. The origin of these entrances goes back to the early church, when the liturgical books and sacred vessels were kept in special storage rooms for safe keeping and the procession was necessary to bring these objects into the church when needed. Over the centuries, these processions have grown more elaborate, and nowadays are accompanied by incense, candles and liturgical fans. In the liturgical theology of the Eastern Orthodox Church, the angels are believed to enter with the clergy into the sanctuary, as evidenced by the prayers which accompany the various entrances.

Clergy are formal leaders within established religions. Their roles and functions vary in different religious traditions, but usually involve presiding over specific rituals and teaching their religion's doctrines and practices. Some of the terms used for individual clergy are clergyman, clergywoman, clergyperson, churchman, cleric, ecclesiastic, and vicegerent while clerk in holy orders has a long history but is rarely used.