[Trithemius, who was the Abbot of Saint James, Herbipolis, was well-known as an avid and learned student of philosophy and occult science. Below, he congratulates his former pupil, Agrippa, on the excellence of his Occult Philosophy, warning him to chose carefully with whom he communicates regarding his work.]

John Trithemius, Abbot of Saint James of Herbipolis, formerly of Spanhemia, to his Henry Cornelius Agrippa of Nettesheim, health and love:

Your work, most renowned Agrippa, entitled Of Occult Philosophy, which you have sent by this bearer to me, has been examined. With how much pleasure I received it no mortal tongue can express nor the pen of any write. I wondered at your more than vulgar learning—that you, being so young, should penetrate into such secrets as have been hid from most learned men; and not only clearly and truly but also properly and elegantly set them forth. Whence first I give you thanks for your good will to me, and, if I shall ever be able, I shall return you thanks to the utmost of my power. Your work, which no learned man can sufficiently commend, I approve of. Now that you may proceed toward higher things, as you have begun, and not suffer such excellent parts of wit to be idle, I do, with as much earnestness as I can, advise, intreat and beseech you that you would exercise yourself in laboring after better things, and demonstrate the light of true wisdom to the ignorant, according as you yourself are divinely enlightened. Neither let the consideration of idle, vain fellows withdraw you from your purpose; I say of them, of whom it is said, "The wearied ox treads hard," whereas no man, to the judgment of the wise, can be truly learned who is sworn to the rudiments of one only faculty. But you have been by God gifted with a large and sublime wit, and it is not that you should imitate oxen but rather birds; neither think it sufficient that you study about particulars, but bend your mind confidently to universals; for by so much the more learned any one is thought, by how much fewer things he is ignorant of. Moreover, your wit is fully apt to all things, and to be rationally employed, not in a few or low things, but many and sublimer. Yet this one rule I advise you to observe—that you communicate vulgar secrets to vulgar friends, but higher and secret to higher and secret friends only: Give hay to an ox, sugar to a parrot only. Understand my meaning, lest you be trod under the oxen's feet, as oftentimes it falls out. Farewell, my happy friend, and if it lie in my power to serve you, command me, and according to your pleasure it shall without delay be done; also, let our friendship increase daily; write often to me, and send me some of your labors I earnestly pray you. Again farewell.