Why be baptized?

. . . he referred [Solomon writing in the Song of Songs] by "Pharaoh" to the implacable foe of our noature, the noxious enemy common to us all whom he drowned in the holy waters of baptism . . .
--Theodoret of Cyr

To which Origen adds:
For it is certain that the evil spirits stir up the temptations and troubles which they arouse against the saints, by means of certain souls who are suitable and convenient for the purpose. Mounting these like chariots, they fiercely attack and assail both the church of God and individual believers.