Gregory the Great — as excerpted in the Catena Aurea on Luke 8:1-3

“(Hom. 33. in Ev.) For what is understood by the seven devils, but all vices? For since all time is comprehended by seven days, rightly by the number seven is universality represented: Mary therefore had seven devils, for she was full of every kind of vice. It follows, And Joanna the wife of Chuza Herod’s steward, and Susanna, and many others who ministered to him of their substance.”