On The Holy Trinity by St. Augustine
Chapter 12.--The Mind is an Image of the Trinity in Its Own Memory, and Understanding, and Will.
19. Are we, then, now to go upward, with whatever strength of purpose we may, to that chiefest and highest essence, of which the human mind is an inadequate image, yet an image? Or are these same three things to be yet more distinctly made plain in the soul, by means of those things which we receive from without, through the bodily sense, wherein the knowledge of corporeal things is impressed upon us in time? Since we found the mind itself to be such in its own memory, and understanding, and will, that since it was understood always to know and always to will itself, it was understood also at the same time always to remember itself, always to understand and love itself, although not always to think of itself as separate from those things which are not itself; and hence its memory of itself, and understanding of itself, are with difficult discerned in it. For in this case, where these two things are very closely conjoined, and one is not preceded by the other by any time at all, it looks as if they were not two things, but one called by two names; and love itself is not so plainly felt to exist when the sense of need does not disclose it, since what is loved is always at hand. And hence these things may be more lucidly set forth, even to men of duller minds, if such topics are treated of as are brought within reach of the mind in time, and happen to it in time; while it remembers what it did not remember before, and sees what it did not see before, and loves what it did not love before. But this discussion demands now another beginning, by reason of the measure of the present book.