De Principiis

Let such, then, be our views respecting those events which appear to befall men, either immediately after birth, or even before they enter upon the light. But as regards the suggestions which are made to the soul, i.e., to the faculty of human thought, by different spirits, and which arouse men to good actions or the contrary, even in such a case we must suppose that there sometimes existed certain causes anterior to bodily birth. For occasionally the mind, when watchful, and casting away from it what is evil, calls to itself the aid of the good; or if it be, on the contrary, negligent and slothful, it makes room through insufficient caution for these spirits, which, lying in wait secretly like robbers, contrive to rush into the minds of men when they see a lodgment made for them by sloth; as the Apostle Peter says, “that our adversary the devil goes about like a roaring lion, seeking whom he may devour.” On which account our heart must be kept with all carefulness both by day and night, and no place be given to the devil; but every effort must be used that the ministers of God— those spirits, viz., who were sent to minister to them who are called to be heirs of salvation — may find a place within us, and be delighted to enter into the guest-chamber of our soul, and dwelling within us may guide us by their counsels; if, indeed, they shall find the habitation of our heart adorned by the practice of virtue and holiness. But let that be sufficient which we have said, as we best could, regarding those powers which are hostile to the human race.