From The Divine Comedy: III. Paradise, Canto V, translated by Dorothy L. Sayers and Barbara Reynolds. Beatrice says to Dante:
Thou must sit still at table long enough
To let digestion work, the which would fain
Have more assistance, for this food is tough.
Open thy mind; take in what I explain
And keep it there; because to understand
Is not to know, if thou dost not retain.