Lots of people use the four Gospels for lots of different things. Ordinarily they are read in the liturgical context of worship, others read them privately for prayer and devotion, still others study them to learn more about the life of Jesus and his disciples.
According to Origen, the great Alexandrian exegete and biblical scholar (ca. 200 A.D.), the Gospels seem to have had another use in the early Church: they were also read in the context of Christian exorcisms, as a means of driving out demonic spirits.
Origen of Alexandria
In his famous work Against Celsus, Origen defends Christians against the pagan charge that they use incantations and the names of demons to drive out demons. Instead, he argues that it is through the pronouncing of Jesus' name and the reading of the Gospel narratives that demons are overthrown:
"Celsus asserts that it is by the names of certain demons, and by the use of incantations, that the Christians appear to be possessed of (miraculous) power; hinting, I suppose, at the practices of those who expel evil spirits by incantations. And here he manifestly appears to malign the Gospel. For it is not by incantations that Christians seem to prevail (over evil spirits), but by the name of Jesus, accompanied by the announcement of the narratives which relate to Him; for the repetition of these has frequently been the means of driving demons out of men, especially when those who repeated them did so in a sound and genuinely believing spirit." (Origen, Against Celsus, 1.6; trans. ANF 4.398).
This gives new meaning to the early Christian teaching that "the word of God is living and active, sharper than any two-edged sword, piercing to the division of soul and spirit..." (Hebrews 4:12). They obviously took this quite literally, seeing the very reading of the Gospel aloud (with faith, of course) as spiritually powerful. "A new teaching, and with exousia!" indeed (Mark 2:27).
It also gives me one more good reason to assign plenty of Gospel reading to my students.