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. (Book I, Chapter 4, Part 1)

Will a master geometer simply forget what he knows? He may not advance further, but the knowledge persists and can be retrieved.

A physical skill will atrophy from neglect or age, but knowledge tends -- unless subjected to accident -- to persist once it is truly mastered.

I am not be a spiritual master, but I cannot imagine how I would lose the spiritual knowledge I now have, or even how I might push it entirely out of mind.

With closer attention and self-sacrifice I could know much more and advance more quickly... and in advancing I might put aside old knowledge for new.

And in any case, the new knowledge would come less from my "habits of industry" and much more from the grace of God.