Shielding spells, sometimes called Warding spells, offer protection against phenomena under the Arcanum’s purview. A Shielding spell might protect against a ghost’s Numina (Death), make the mage immune to fire (Forces) or disease (Life), or allow her to survive in a caustic atmosphere (Matter).
Mages protect themselves from general harm through the power of their Arcana with the Mage Armour Attainment rather than Shielding spells.
In Game:
This is what separates a squishy mortal body from all the arcane and mundane phenomena that would kill a Sleeper.
Any mage who engages in combat on a regular basis (or who, because of position or even just paranoia, fears being attacked) or deals with powerful supernatural phenomena has a use for Shielding spells.
Some of the most treasured of Artifacts and Imbued Items are enchanted with Shielding magics in addition to their normal Mage Armour. Quite simply, no willworker with an ounce of good sense turns up her nose at the idea of a little extra protection.
Note that Shielding spells do “stack” with mundane, or even enhanced, Imbued or Artifact armour, though not with one another. This means that a mage with a well-crafted suit of armour and a powerful Shielding enchantment is virtually untouchable in combat, save by those magics that ignore or otherwise circumvent armour.
In Story:
Reading minds, soaring on the wind and distilling the complexities of the Tapestry are all well and good, but one of the first and most pressing human drives is the desire to possess the means to defend oneself. Some scholars maintain that Shielding magics were not always as subtle and refined as they are, for the most part, today, and that some great willworkers of old conjured up armour of writhing flame, fragmented space and ferocious gales.
Still, what accounts there are of such things now are unclear at best, and may be nothing more than rumour and legend. With the rise of Paradox and the Fall of the First City protective magic had to become more and more subtle.
As in ancient days, most modern mentors will not send their students out into the world until they have demonstrated the ability to make use of the Mage Armour Attainment and the Practice of Shielding for at least one Arcanum. For the most part, it is considered criminally irresponsible for an Awakened teacher to allow a new willworker to face the perils of her new life undefended by the auspices of this Practice.
In fact, there are those of all five orders who will assist a prematurely released newly Awakened mage in learning at least one Mage Armour, should she not know one, without asking for any favour in return, so basic an obligation is it considered. There are, if rumours are to be believed, even Seers of the Throne who will do so.
As a mage grows more comfortable in her Awakened existence, the Practice of Shielding helps her to feel confident in her dealings with others. She has less need for fear of casual violence and can treat with even considerably more experienced (and, thus, dangerous) willworkers with an increased feeling of safety. When she is sufficiently skilled in an Arcanum, she can go about her business, knowing that most Sleepers are virtually incapable of causing her harm at all.