The Cleric's Robes is a mid to high-ranked mystic armor in Final Fantasy XII that boosts the wearer's Defense by 50 (Zodiac) or 37 (original), and Magick Power by 9. In the Zodiac versions, it also gives 70 MP.
In the original PlayStation 2 version, the Cleric's Robes is sold for 10,700 gil in Balfonheim Port after the party has the Treaty-Blade. It is also found as a treasure in Barheim Passage's The Zeviah Span (at the south end; 70% chance to appear, 50% chance for gil, 50% chance the item treasure is the Cleric's Robes without the Diamond Armlet equipped ). It is also rarely poached from the Vivian.
In the updated Zodiac versions, the Cleric's Robes is sold in Balfonheim for 10,700 gil after the party has the Treaty-Blade. It is a treasure in Ridorana Cataract's Echoes from Time's Garden (75% chance to appear, 50% chance for gil, 50% chance the item treasure is the Cleric's Robes without the Diamond Armlet equipped). It is still a rare poach from the Vivian.
Cleric's Robes is a mid to high-ranked mystic armor, giving 50 or 37 Defense depending on version, and 9 Magick Power, as well as 70 MP in the Zodiac versions. Mystic armor offer magick-related bonuses that affect all types of magickal actions, from casting black magick to damage an enemy, to casting white magick to heal the party. Magick Power is also a factor when determining damage dealt by katana, staves, and maces.
In the Zodiac versions, White Mage, Red Battlemage, Black Mage, and Bushi can equip it, and so the Cleric's Robes is only useful to buy if the player has chosen any of these License Boards for their party. In The Zodiac Age versions, after fighting Belias the player can choose two License Boards per party member; it is usually a good idea to pair jobs that use two different types of armor for versatility.
The Cleric's Robes is the best mystic armor the player can buy in the Zodiac versions. It could thus be used for endgame gear, but it would likely be worthwhile to look for some of the better ones that are not purchasable, as the White and Black Robes' elemental-boosting properties can massively affect damage-per-second with certain weapons, and the Glimmering and Lordly Robes have superior stats. In the original PlayStation 2 version, only the ultimate robe, the Lordly Robes, can't be bought from a shop.