Mask of Law and Grace

Protection from two colors stapled to a single white mana, with no rider to pay it back. The interesting choice is which two: black and red, the colors that historically owned the cheap point removal and the burn. Protection from black blanks targeted destruction and lets the creature ignore black blockers in combat; protection from red turns off burn aimed at the creature and lets it ignore red blockers. Bundling both onto one aura makes this a focused answer to the two colors most likely to kill your creature cheaply, which is also the structural weakness of any aura: spend the mana, commit the card, and a single bounce that returns the host to hand or a sweeper that does not target sends the aura to the graveyard for no longer enchanting anything. The protection grants have hard edges, too. Neither color word touches noncombat sweepers from other colors, and protection from black does nothing against edict effects, which target the player rather than the creature and force a sacrifice the controller chooses. The same goes for any other sacrifice clause: protection shields against being targeted, not against being chosen. The card reads as a clean expression of protection-as-shield: cheap, narrow, and entirely dependent on knowing exactly what you are protecting against before you cast it.