While nobles wage their petty wars, rogues scrounge for ill gotten wealth, and friars preach to their forlorn flocks, a mystical order of wizards dwells in the outskirts of civilization, dedicated to their own arcane pursuits. Gathered together by the enigmatic Order of Hermes, these wizards struggle against both internal intrigue and persecution of those that do not care to understand their art. As sages of great wisdom and lore, and as sorcerers of immense power, they face the perils that few others dare to speak of. They barter with the faerie lords, gather the sundry magical ingredients for their rituals. And experience the subtle beauty of their enigmatic realm. Though magic pervades this medieval world, only a few gifted individuals given years of apprenticeship, have ever mastered the art of magic.
Magic pervades every aspect of a magus’ life. Once you open the Pandora’s box of magical knowledge, it grows and develops within your heart, as if it had a life and purpose of its own, altering your view of the world., your understanding of society and your understanding of yourself. Magi must constantly strive to remain in control of their lives, for if they are lax or if they attempt to perform magics yet tooo powerful for them, their magic powers will grow stronger than they are, and they will be swallowed up. Among members of the Order, this is known as “wizard’s twilight”.
Wizards dream far more than other mortals. Their intense connection to magic invades even their sleep, and in their sometimes tortured dreams they delve once again into the mysteries of magic that are so much part of their waking hours.
So thoroughly is a magus changed by magic that most magi see the world in terms of their arts. They see in everything and everyone potential subjects for their spells.
Insensitive to the distractions that occupy mortals, such as the pursuit of gold or the need to be accepted and respected within society, magi are free to pursue their studies single-mindedly, and their extended lifespan do little to slow their search for knowledge. For wizards to succeed, they must become obsessed with uncovering the secrets of magic and of gaining power over it.
Common people do not trust wizards, most of whom give off a subtle but undeniable air of somehow being different. They are too inhuman to be ready objects for such human emotions as affection and trust. Magi wear strange robes and carry impressive staffs to display their status and increase the awe felt by those who see them.
Magi are forever distant from the simple life enjoyed by the common folk. They see their grogs dancing to high-spirited pipes, frolicking in summer fields , and singng bawdy drinking songs, but they know such pleasures are denied to them. . The spells that protect them from magic also keep out the daily enchantments of a haunting songs or a beautiful face. A magus heart is usually barred against the beauty of everyday life.
These wizards are isolated from society and so understand little of it; the common folk of a village that lies down stream from their tower are as foreign to them as a Saracen or infidel would be. Wizards are far more comfortable working in a cramped, chill laboratory than listening to a troubadour’s flowing verse or dancing with a beautiful maiden.
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Bonus points and a virtual CrHe cookie for the first one to spell the author and origin of this text. 
I found this text highly inspiring. Current canon has heavily deviated from it, and most magi seem to be far more “earthly” (terrenal?) than what this text describes. However, I liked a lot some of the imagery described here and I am sending it to my troupe. This is the kind of background text that makes Ars Magica something else, and not “just another fantasy medieval setting” to me. 
This disconnection of magi from mundane society was especially attractive to me. Gives them a king of eeriness that they currently lack IMS. In fact they have never had it much. This insight into the psyche of the magi is highly enlightening to me.
The code is much more sensible if you take this text as reference instead of the current depiction of the OoH vs whatever interactions.
Cheers,
Xavi