Crux sacra sit mihi lux
Non draco sit mihi dux
Vade retro satana
Numquam suade mihi vana
Sunt mala quae libas
Ipse venena bibas
A Priest in the Roman Catholic Church was considered to have received authority directly from the Pope in Rome, God's representative on earth. Because of this, during the Mass, the Priest had the power to consecrate the Host and the Wine, so that they were transformed in our material world into the Body and Blood of Christ. But there were other powers the Priest had. Besides talking directly to God and causing God and angels to intervene in the world of man, a Priest also had the power to talk to Satan and to demons. He could exorcise Satan and demons from a person, and also make them do his will in other ways - he had the power to control them. One particular grimoire, The Grimoire of Honorius, was designed for use specifically by Priests, and included saying the Mass and consecrating the Host as part of the rituals.
Ritus Exorcizandi Obsessos a Daemonio
(Instructions for a Roman Catholic priest to talk to and command Satan and demons possessing a person.)
Grimoires
(Instructions for Catholic Priests to invoke and harness the power of Satan and demons to do their will.)