De Principiis: Book I 4On Defection, or Falling Away.

1. To exhibit the nature of defection or falling away, on the part of those who conduct themselves carelessly, it will not appear out of place to employ a similitude by way of illustration. Suppose, then, the case of one who had become gradually acquainted with the art or science, say of geometry or medicine, until he had reached perfection, having trained himself for a lengthened time in its principles and practice, so as to attain a complete mastery over the art: to such an one it could never happen, that, when he lay down to sleep in the possession of his skill, he should awake in a state of ignorance. It is not our purpose to adduce or to notice here those accidents which are occasioned by any injury or weakness, for they do not apply to our present illustration. According to our point of view, then, so long as that geometer or physician continues to exercise himself in the study of his art and in the practice of its principles, the knowledge of his profession abides with him; but if he withdraw from its practice, and lay aside his habits of industry, then, by his neglect, at first a few things will gradually escape him, then by and by more and more, until in course of time everything will be forgotten, and be completely effaced from the memory. It is possible, indeed, that when he has first begun to fall away, and to yield to the corrupting influence of a negligence which is small as yet, he may, if he be aroused and return speedily to his senses, repair those losses which up to that time are only recent, and recover that knowledge which hitherto had been only slightly obliterated from his mind. Let us apply this now to the case of those who have devoted themselves to the knowledge and wisdom of God, whose learning and diligence incomparably surpass all other training; and let us contemplate, according to the form of the similitude employed, what is the acquisition of knowledge, or what is its disappearance, especially when we hear from the apostle what is said of those who are perfect, that they shall behold face to face the glory of the Lord in the revelation of His mysteries.

2. But in our desire to show the divine benefits bestowed upon us by Father, Son, and Holy Spirit, which Trinity is the fountain of all holiness, we have fallen, in what we have said, into a digression, having considered that the subject of the soul, which accidentally came before us, should be touched on, although cursorily, seeing we were discussing a cognate topic relating to our rational nature. We shall, however, with the permission of God through Jesus Christ and the Holy Spirit, more conveniently consider in the proper place the subject of all rational beings, which are distinguished into three genera and species.