The startling image I've added here, from The Lion and the Cardinal, depicts a scene reminiscent of Anselm's analogy: the four Evangelists pouring scripture into a great mill, which provides sustenance for all, the four strips of verses being fused into one, that diatesseratic verse itself flowing into the hand of the Logos, the incarnate Word
Why is this metaphor so apt, and so typical of the Anselmian approach to the right use of the mind? One of his letters, in which he touches on his moral theory, is particularly relevant (Letter 414, to Robert and a small community of nuns)Chapter 41. A resemblance between the human heart and a grinding millIndeed, our heart is similar to an ever-grinding mill, which some lord gave to one of his servants so that he might guard it, prescribing for him that he should grind his provisions, namely grain or barley or even wild oats, in it, and live on what he has ground. Truly, one who always plots against this mill behaves as an enemy to this servant. When this enemy finds the mill to be empty, he either straightaway casts sand into it, which wears it away, or pitch, which gums it up, or something else which soils it, or fills it up with chaff.
So, if this servant guards his mill well, and grinds in it so much provisions as his lord gives him for sustenance, then clean flour of each kind of provision, ground up in the mill, will come out of that same mill. And, precisely because he grinds, and serves his lord, he acquires for himself his means of life. But, if he permits his enemy to mess up [violare] his mill, bad flour will come out of it, since the provisions he grinds are bad. But, this flour greatly displeases that lord, and the servant does not gain his means of life, but rather instead hunger.
Now, this ever-grinding mill is the human heart, assiduously thinking about something. And God apportions it to each of his human servants, commanding that they turn over and over such thoughts as he himself suggests to them. And of these thoughts, some are like grain, others like barley, and others like wild oats.
Indeed pure thoughts, which the soul turns over when it thinks purely about God in settled contemplation, are like grain.
And those, by which one by meditating prepares oneself to ascend from one virtue to another, are like barley. And, these thoughts, even though they are good, are less perfect than the first and higher ones.
Now, those by which a person intends to put aside their vices, are like wild oats. For these are good, but still more imperfect than the other two kinds. Still, God wills all of these, so that a person turns them over in his or her heart, and from them gains for themselves a means of eternal life.
But, because the devil always strives against human beings, he always plots against their hearts. So, if at some time he discovers the human heart empty of good thoughts, he immediately fills it up, if he can, with bad ones. Of these evil thoughts, some of them wear away the human heart, like anger and envy; others gum it up and pollute it, like gluttony and prodigality; others take possession of it, like vain things that are not greatly damaging.
And so, if this person guards their heart well, and turns over holy thoughts in it, clean words will come out of their mouth just like from the hole of a mill, and clean sight through their eyes, clean hearing through their ears, clean tastes through their mouth, clean odors through their nostrils, clean touch through all of the body, in accordance with the kinds of clean thoughts which they inwardly turn over and over. And, from these clean thoughts, one zealously serves God by thinking them, and one gains eternal life for oneself.
If, however, one permits the devil to corrupt ones heart, quickly the vices make their way in through the senses, connected to the types of bad thoughts which are inwardly turned over and over. And these both greatly displease God and a person does not acquire his or her means of life from them, but rather death. For, when everyone comes to the end, so much of good or evil they have then ground, that much [eternal] life or death they will discover to be prepared for them.
Do not struggle with wicked thoughts or with a wicked intention, but when they molest you do your utmost to occupy your mind with some useful thought and intention until they disappear. for no thought of intention is ever driven out of your heart except by some other thought or intention which does not agree with it. Therefore, be so disposed towards useless thoughts and intentions that by attending with all your might to profitable ones you mind may refuse to remember them or rake any notice of them.