“…the souls that aspire to perfection are the object of [the devil’s] special attacks. Sinners, given up to their passions, are an easier conquest; this the devil rules peacefully over an immense throng of souls that he does not disturb in any way… The action of the devil against souls eager for perfection is not, then, a rare event; it is normal and frequent. It becomes particularly intense “when the devil sees that the soul’s character and habits are such that it is ready to make further progress: all the powers of hell will combine to drive it back again,” asserts St. Teresa (Interior Castle, Mansion II)”
from “I Want to See God”, by P. Marie-Eugene, OCD, Vol I; Christian Classics, Notre Dame, Indiana, 1953, p103.