Channellers, like all other mages, know what kind of wear and tear their hazardous lifestyles can exact on garments or gear. Blasts of fire, spills of acid, and sizzling lightning are day-to-day occurances with them. After learning to channel the energy from inside an object to them, they learn how to pull the energy from outside the object, thereby pulling some of the harmful energies -- kinetic, thermal, whatever -- to them. While this can (and indeed often does) hurt quite a lot, flesh heals and steel doesn't. Channellers often cast this spell on their prized golems, but it will work on just about anything. You can cast this spell at yourself to check how many shields are still active.